4.5 Nuclear and Particle Physics

Tracks of charged particles

A charged particle interacts with a stationary proton at P. This produces two neutral particles. Each of these neutral particles is unstable and decays into other particles. Explain the evidence provided by the diagram for this description of the particle interactions (3)

📚 Jan 2024

• There are no tracks after P
• (Only) charged particles leave tracks // Uncharged /neutral particles leave no tracks
• ‘V’ points on photograph identified as subsequent decays

State 2 ways that the diagram shows the kaon is neutral

📚 Jun 2022

• Kaon does not leave a track
• Pions have opposite charge and charge is conserved

Explain the process that enables a particle detector to detect charged particles (2)

📚 Jan 2022

• (the particle is) ionising Or it knocks electrons out of atoms in its path
• A track is formed by the ionised particles produced

Explain whether the maximum acceleration would be the same as for the alpha particle reflected back through 180 degree (4)

📚 Jan 2021

• alpha particle does not ever have zero speed/ke
• so not all of the energy has been transferred from the kinetic energy store to the electric potential energy store
• it is not as close to the nucleus Or minimum r is greater
• so (max) force is less, so (max) acceleration is less

Alpha particle scattering experiment

The interaction at P is neutral DSCBE the observations from these experiments and the conclusions that were made from these observations (5)

📚 Jan 2024

• Most alphas went straight through // Most alpha particles were undeviated
• So atom is mainly empty (space) (MP2 dependent on MP1)
• A few alpha particles were deflected by small angles
• very few alpha particles had a deflection > 90° // Very few alpha particles came straight back
• There is a concentration of charge in the atom (MP5 dependent on MP3 or MP4) // There is a concentration of mass in the atom

State 3 observations and the corresponding conclusions made from the alpha particle scattering experiment (6)

📚 Jun 2022

• Most alpha particles were undeviated Or Most particles pass through with little or no deviation
• Most of the atom is empty space (MP2 with reference to lack of deviation)
• Few alpha particles were scattered by small angles
• There is a concentration of charge in the atom (MP4 with reference to scattering)
• Very few alpha particles were deviated by more than 90°
• Most of the mass is concentrated in a small region of the atom
• Or Most of the mass is concentrated in nucleus (Accept Mass of nucleus much greater than mass of alpha particle) (MP6 with reference to back scattering)

*Following these experiments Rutherord said, “it was almost as incredible as if you fired a 12-inch shell (large missile) at a piece of tissue paper and it came back and hit you.” Explain why Rutherford was surprised at the results of the experiment and how this led to the nuclear model for the atom (6)

📚 Oct 2021

• IC1 plum pudding model of atom prior to experiment Or J J Thomson model of atom prior to experiment Or atom believed to have an equally distributed mass/charge throughout
• IC2 alpha particles expected to go straight through Or alpha particles expected to have only a small deflection
• IC3 a small number of alphas deflected through very large angles Or a small proportion of alphas come straight back
• IC4 (changed to) model of the atom having very small nucleus Or (changed to) model of atom where most is empty space
• IC5 nucleus contains (almost) all the mass
• IC6 nucleus is charged

Explain why the thickness of the gold foil had to be very small (2)

📚 Oct 2021

• Either
• a thin sheet would contain few layers of atoms
• so alpha particles would be less likely to undergo multiple deflections Or so alpha particles would be less likely to be absorbed
• OR
• alpha particles are strongly ionising
• so alpha particles can only penetrate a thin sheet or so alpha particles have low penetration

Explain how the results of the experiment led to this conclusion (atom has central charge contained in a very small volume) (2)

📚 Oct 2020

• Only a few particles were deflected
• So only a few came close enough to be deflected (so the charge must occupy a small volume)

Rutherford wrote, “the main deductions from the theory are independent of whether the central charge is positive or negative.” Discuss why the observations did not allow Rutherford to conclude whether the central charge is positive or negative (4) You may wish to use diagrams to illustrate your response.

📚 Oct 2020

• Alpha particles close to a –ve nucleus would experience a force towards it and be deviated slightly (ii)
• Alpha particles close to a +ve nucleus would experience a force away from it and be deviated slightly (v)
• Alpha particles very close to a –ve nucleus would experience a force towards it and be deviated right around it and back again (iii)
• Alpha particles approaching a +ve nucleus directly would experience a force away from it and be deviated right back again (vi)
• All of the possible observed paths can be explained by both types of nucleus, so the suggestion is correct

State why the alpha source and gold foil were contained in a vacuum (1)

📚 Jan 2020

• So no collisions with air molecules // so the air doesn’t stop alpha particles from reaching the detector

Discuss the extent to which the results of the alpha particle scattering experiments justified replacing the plum pudding model with a nuclear model of the atom (6)

📚 Jan 2020

• Most alpha particles passed straight through the gold foil
• Some alpha particles were deflected by small angles
• Either model would predict small or zero deflections because in the nuclear model the atom is mostly empty space and in the ‘pudding’ model matter is too spread out
• A few proportion of alpha particles were deflected by more than 90d
• This did not fit the plum pudding model as this deflection requires a high concentration of charge (to provide a large force) // this can only be explained by the nuclear model as this deflection requires a high concentration of charge to (produce a large force)
• This did not fit the plum pudding model as this deflection requires a high concentration of mass // this could only be explained by the nuclear model as this deflection requires a high concentration of mass (so that the alpha particle is deflected and not the gold nucleus)

Deduce quark structure

Explain the quark structure of a K- meson (2)

📚 Jan 2024

• s u̅
• The meson must be a quark-antiquark pair and include a strange quark
• // The meson must be a quark-antiquark pair and have a charge of −1

How a cyclotron works

Explain how the cyclotron produces a beam of high energy particles (4) Refer to the alternating potential difference and 2) the magnetic field

📚 Jan 2024

• accelerates particles
• gives particles energy
• Magnetic field / force at right angles to particles path
• Magnetic field/force maintains circular motion (whilst in dees)
• // Particle experiences centripetal force / acceleration (whilst in dees)
• switches every half cycle
• // Polarity of dees switches every half cycle
• switches when particle is in dees
• has a constant time period
• has a constant frequency
• // period is independent of speed of particle

Explain why a magnetic field is applied at right angles to the dees in the cyclotron (2)

📚 Jun 2023

• The particles experience a force at right angles to their motion/path/velocity.
• Which causes centripetal acceleration/force // Which causes circular motion

*Explain the role of electric and magnetic fields in the production of high-speed charged particles by a cyclotron (6)

📚 Jan 2021

• Magnetic field perpendicular to velocity of particles
• Magnetic force on particles perpendicular to velocity
• Particles experience centripetal acceleration/force so they undergo circular motion
• Alternating potential difference between dees changes direction while particle in dees
• Particle accelerated by electric field between dees
• (Electric) field in correct direction so that force on particle further increases speed

Explain the significance of the expression obtained by Lawrence to the operation of a cyclotron (4)

📚 Jan 2020

• Time independent of speed // radius
• So particles take constant time to complete circular path // particles spend the same time in each dee
• So a fixed frequency can be used for the pd
• / field across the gap will be in the correct direction to increase the speed the speed of the particles as they cross each time

Conservation laws

Explain 2 other conservation laws that apply to this decay (4)

📚 Oct 2023

• Any two pairs of:
• (Conservation of) charge
• −1 → −1 + 0
• (Conservation of) lepton number
• 0 → 1 + −1
• (Conservation of) baryon number
• 0 → 0 + 0

Explain whether the following decay would be possible (3)

📚 Jan 2023

• You should consider conservation of charge and lepton number
• Charge of particles shown: –1, –1, 0, 0
• Lepton number of particles shown: 1, 1 ,1, –1
• Charge conserved and lepton number conserved, so possible // But muon lepton number: 1 does not = –1, not obeyed, so not possible // But electron lepton number: 0 does not = 1+1, not obeyed, so not possible

Deduce the charge and the baryon number for the omega particle (3)

📚 Jan 2022

• applies charge conservation
• omega baryon charge −1
• baryon number: before = 1 identified as the proton so the omega particle = 1

*The rest mass of the omega baryon is significantly larger than the rest mass of the proton. Discuss how energy and momentum are conserved during this collision (6)

📚 Jan 2022

• Energy:
• IC1 As (Rest) mass-energy of proton and kaon + Initial \(E_k\) = (rest) mass-energy of omega and kaon + kinetic energies of both particles
• Or (Total) mass-energy conserved
• IC2 Incoming \(K^−\) had high kinetic energy
• IC3 some of this initial kinetic energy converted to mass of the omega particle (– mass of proton)
• IC4 \(∆E = ∆mc^2\)
• Momentum:
• IC5 momentum of \(K^−\) = sum of x components of \(K^+\) + \(Ω^−\)
• Or vector sum of momentum of \(K^+\) + \(Ω^−\) = momentum of \(K^−\)
• Or an attempt to sketch a triangle of vectors (be exact, give example)
• eg
• IC6 y component of \(K^+\) equals y component \(Ω^−\) Or all vectors correctly labelled

A student correctly suggests that this collision cannot lead to both particles being omega baryons, as this breaks a conservation law. Discuss the student’s suggestion (3)

📚 Oct 2021

• If both omega, it would break the conservation of baryon number
• Must be omega and anti-omega
• Further detail of baryon number: If both omega, before collision baryon number = 0 and after collision baryon number = 2 (which breaks conservation law) Or If omega and anti-omega before collision baryon number = 0 and after 1 – 1 = 0 (which obeys conservation law)

Explain how this equation shows that the decay obeys three conservation laws (6)

📚 Jan 2021

• Conservation of charge (because same before and after)
• Antineutron charge = 0; charge of antiproton = –1, positron = 1, neutrino = 0; total charge after = 0
• Conservation of baryon number (because same before and after)
• Antineutron baryon number = –1; Antiproton baryon number = –1, positron = 0, neutrino = 0, Total baryon number after =–1
• Conservation of lepton number (because same before and after)
• Antineutron lepton number = 0; Antiproton lepton number = 0, positron = –1, neutrino = 1, Total lepton number after = 0

Explain the assumption made when applying the principle of conservation of momentum to collisions (2)

📚 Jan 2021

• The assumption is that no (resultant) external forces act
• Because if external forces act there will be acceleration, so the final momentum will be different than otherwise Or if external forces act there will be an (additional) impulse, so the change in momentum will be different

Relativistic effects

Explain how the average lifetime of these high-energy pions compares with the lifetime of pions at rest (2)

📚 Oct 2023

• (When v = 0.99c) relativistic effects will be significant
• // (When v = 0.99c) time dilation occurs
• The lifetime (of high energy pions) would be longer (than for pions at rest)

Most types of quark form hadrons on a timescale of \(10^{-23}\)s. The top quark does not form hadrons because its lifetime is only \(10^{-25}\)s. A student suggests that, if the top quarks travelled at relativistic speeds, it could be possible for them to form hadrons. ASSESS this suggestion (2)

📚 Jan 2023

• (An observer will see an) increased lifetime
• But the time to form hadrons would also increase as seen by the observer, so it is incorrect // the lifetime would not increase as seen by the top quark, so it is incorrect

Z bosons produced by high energy collisions can have a range of lifetimes. The Z bosons with the longest lifetimes are those that were moving very fast. (2) Explain this observation.

📚 Oct 2022

• At speeds close to the speed of light
• There is a relativistic increase in lifetime Or time dilation occurs

Stationary muons are unstable and have a mean lifetime of a few microseconds. Explain why muons in the ring are observed to have a much greater mean lifetime. (2)

📚 Jan 2022

• muons travelling close to speed of light
• relativistic effect on particle lifetime

Most of the particles detected in the spark chamber are muons. The muons were created in the upper atmosphere. Muons normally have a very short lifetime and should have decayed before they reach the surface of the earth. Explain why these muons reach the surface of the earth (3)

📚 Oct 2021

• muons travelling close to speed of light
• relativistic effect increases particle lifetime (for observer)
• so travels further than normally expected (before decaying)

Explain whether these observations are consistent with ideas from relativity (5)

📚 Jan 2021

• The speed of the muon is very close to the speed of light
• Calculate distance travelled at 0.994 c in the average lifetime (without relativistic effects) = 656 m Or Calculate the time to travel 1600 m at 0.994c = 5.4 x 10-6 s
• Comparative comment about calculated value and situation if no relativistic effects
• Comment about lifetime linked to relativistic effects Or Comment about time of flight linked to relativistic effects
• Reason why most reach the ground

How a LINAC works

Explain the use of electric fields in a linac (4) Refer to the frequency of the a.c. supply

📚 Jun 2023

• The particles are accelerated by an electric field in the gaps
• frequency is constant so the particles spend the same time in the tubes/gaps
• (This is achieved by) increasing length of drift tubes // (This is achieved by) increasing length of gaps
• The (a.c) polarity changes so the (electric) field is in the same direction when the particle is in the gaps // The (a.c.) polarity changes so it is always accelerating the particles

*Explain why the distances between consecutive tubes increase in the first section of the linac but are almost equally spaced in the last section of the linac (6)

📚 Jun 2022

• ​​IC1 Electrons accelerate in the gaps
• supply is constant
• IC3 Time taken for an electron to travel between (consecutive) tubes is constant (and they are accelerating)
• electrons travel further in a fixed time with a higher speed
• IC5 (In the last section of the linac) the electron approaches the speed of light
• IC6 Speed becomes (almost) constant so distance travelled in a fixed amount of time becomes (almost) constant

Explain why the arrangement of linac works with a constant frequency a.c. supply (4)

📚 Oct 2021

• The beam/electron/positron is gaining speed
• The length of tubes increases or the length of gaps between tubes increases
• So time between beam exiting (successive) tubes is constant Or time spent in each tube is constant Or time spent between (each successive pair of) tubes is constant
• has to reverse in this time period and hence frequency is constant

For very high energy electrons, successive drift tubes have the same length. Explain why (2)

📚 Oct 2020

• As the electrons approach the speed of light there is no appreciable increase in speed
• v is constant and the electrons spend the same time in(/between) drift tubes, so s = vt must be constant

Standard quark-lepton model

Explain why the existence of a sixth quark was predicted (3)

📚 Jan 2023

• 1st generation, u and d, are a pair and 2nd generation, s and c, are a pair
• So 6th quark is a pair with b
• By symmetry of the standard model

DSCBE the structure of a baryon and a meson (2)

📚 Jan 2022

• A baryon is made of 3 quarks
• A meson is made of 1 quark & 1 antiquark

The muon belongs to the same family of particles as the electron. State how the muon is classified in the standard model (2)

📚 Jan 2022

• It is a lepton
• It is a fundamental particle Or second generation

State the properties of a positron that show it is the antiparticle to the electron (3)

📚 Jun 2021

• Mass equal (to mass of electron)
• Charge equal and opposite (to charge of electron)
• Lepton number (equal and) opposite (to lepton number of electron)

Explain why muons are not described as mesons in the standard model (2)

📚 Jan 2021

• Muons are leptons Or Muons are fundamental/elementary particles
• but mesons are made of quarks Or mesons are made of quark-antiquark

Compare this model with the current standard model (4)

📚 Oct 2020

• Similarities
• Zweig model, baryon 3 aces and standard model baryon 3 quarks, so similar
• Zweig model, meson 2 aces and standard model meson 2 quarks, so similar
• Zweig model, number of aces same as lepton and standard model quarks same as leptons, so similar
• Zweig model, aces have fractional charge and standard model quarks have fractional charge, so similar
• Zweig model, aces are fundamental and standard model quarks are fundamental, so similar
• Zweig model, aces have baryon number 1/3 and standard model quarks have baryon number 1/3, so similar
• Differences
• Zweig model, meson 2 aces but standard model meson quark antiquark, so different
• Zweig model, 4 aces in total but standard model 6 quarks in total, so different
• Zweig model, 4 leptons in total and standard model 6 leptons, so different
• Zweig model, no anti-aces but standard model has anti-quarks, so different

DSCBE how the underlined particles (electron, proton, neutron, meson, muon) fit into the standard model (6)

📚 Jan 2020

• Neutrons / protons are baryons
• baryons/ neutrons / protons made of 3 quarks
• Mesons made of quark and antiquark
• Electrons / muons are leptons
• p/n/e first generation // muon second generation
• Leptons / electron / muon / quarks fundamental // proton / neutron / mesons not fundamental

Collision of particle

Explain the advantage of colliding beams of particles (4)

📚 Jan 2023

• If target is stationary there is resultant momentum, so products must have resultant momentum after collision
• So products must have high kinetic energy
• (Therefore) less/little energy available for formation of particles
• (so) less massive particles formed
• OR
• If beams collide there is zero resultant momentum, so products may have no/low momentum after collision
• So products do not have high kinetic energy
• (Therefore) all/most/more energy available for formation of particles
• (so) more massive particles formed

Protons and anti-protons were accelerated in the Spp_barS to very high energies before they collided. (3) Explain why the protons and anti-protons needed high energies to produce the Z boson

📚 Oct 2022

• Mass-energy is conserved Or refers to \(ΔE = c^{2}Δm\)
• Need for large amounts of energy to create a high-mass particle Or Need more energy because mass of Z much greater than mass of proton(s) [accept 97 times]
• (Additional) energy comes from the kinetic energy of colliding particles

Explain why high energy particles are required to investigate the structure of the nucleons (3)

📚 Jan 2020

• High energy so particles have large momentum
• High momentum so that de Broglie wavelength is small
• Studying nucleons requires wavelengths of the order of nucleon size

Range and penetration of alpha, beta, gamma particles

Alpha particles were chosen by Rutherford for large-angle scattering experiments. Explain why alpha particles are more suitable for these experiments compared to beta particles or gamma rays (3)

📚 Oct 2022

• Alpha has double the charge (of beta)
• So for alpha deflecting force will be more (for same separation)
• Beta particles are much less massive than alpha particles
• So beta might be deflected by the electrons (surrounding the nucleus of gold)
• Gamma isn’t charged
• So gamma will not deflect at all (electrostatically) Or gamma will not experience any electrostatic force
• Gamma more penetrating
• So gamma less likely to interact

Spiral track

Explain how the diagram shows that the anti-muon is travelling in a clockwise path (3)

📚 Oct 2021

• The radius of the (spiral) path decreases (following it clockwise)
• The momentum/velocity/speed of the particle is decreasing
• as energy is transferred from the anti-muon (by ionisation and electromagnetic radiation)

Tracks of charged practicles

State a reason why radon atoms do not leave tracks (1)

📚 Oct 2020

• They are uncharged Or they do not cause ionisation

Deduce which track is for the first alpha particle emitted (3)

📚 Oct 2020

• There is a gap between the start of the two tracks
• The atom/ion/nucleus produced after alpha decay would recoil in the opposite direction before emitting the next alpha
• So we can tell that the track on the right was produced by the first alpha
• OR
• The track on the right is thicker (than the track on the left)
• This means that the track has had a longer time in which to disperse
• So we can tell that the track on the right was produced by the first alpha

4.4 Electric and Magnetic Fields

Data inferences

Explain how the time taken to charge the capacitor would change (3) You do not need to do any further calculations

📚 Jan 2024

• Resistance in circuit would decrease
• So current in circuit would increase // so time constant will decrease // so T = RC will decrease
• (Hence) capacitor would charge more quickly
• MP2 dependent on MP1, MP3 dependent on MP2

Explain the extent to which the students’ results support this statement (3)

📚 Jan 2021

• The maxima are integer multiples of \(1.6 × 10^{−19} C\) Or The peaks are at intervals of \(1.6 × 10^{−19} C\)
• The spread about the maxima is small
• This could be due to experimental error, so the statement is supported

Explain how the behaviour of the LED shown in the graph will affect the time taken for the light intensity to decrease to zero (3)

📚 Jan 2020

• From the graph, as pd decreases the resistance increases
• Therefore the time constant increases
• The light will take longer to switch off

Explain the changes in the graph when the angular velocity of the coil is halved (2)

📚 Jan 2020

• (Half angular velocity) so takes twice as long to turn, so period halved
• (Half angular velocity) so rate of change of flux halved so emf halved

Electromagnetic induction

*Explain why the kettle heats up when there is an alternating current in the coil (6)

📚 Jan 2024

• IC1 The current produces a magnetic field
• IC2 Alternating current, so alternating/varying magnetic field
• IC3 There is a change of flux linkage with kettle/core due to the
• alternating current // Lines of magnetic flux cut the kettle/core.
• is induced across the kettle/core
• IC5 Currents circulate in (the iron of) the kettle/core
• IC6 The kettle heats as energy is dissipated by the heating effect of currents // the core heats as energy is dissipated and the thermal energy is transferred to the kettle by conduction

A bar magnet was dropped vertically through a small coil. *Explain the variation of emf with time (6)

📚 Oct 2023

• IC1 There is a change in flux linkage (with the coil)
• // the wires cut the magnetic field (lines)
• IC2 The greater the RATE of change of flux linkage the larger the induced e.m.f.
• IC3 After the south pole REACHES the coil the flux linkage (starts to) decrease
• // When the south pole reaches the coil, by Lenz’s law the polarity of the coil changes to continue to resist the motion of the magnet
• // As the south pole reaches the coil the rate of change of flux linkage is zero
• is negative
• IC5 The (downwards) speed of the magnet increases
• IC6 Emf is zero before magnet enters coil
• // Emf is zero when midpoint of magnet in coil
• // Maximum negative value is greater than maximum positive value
• // Time for which emf is negative is greater than time for which emf is positive
• // emf is zero when magnet totally leaves coil

Explain why a p.d. was produced as the coil was rotated (2)

📚 Jun 2023

• (Wires) cut lines of magnetic FLUX // flux linkage (with coil) changing
• Induces emf

*When the student moved the wire quickly downwards between the magnets, the reading on the balance changed. Explain how the reading on the balance changed (6)

📚 Jan 2023

• IC1: Wire cuts lines of magnetic flux // Wire cuts magnetic field lines // flux linkage of wire changes
• IC2: Induces e.m.f.
• IC3: so current in loop of wire
• IC4: Current in a wire in a magnetic field experiences a force // Magnetic field associated with this current
• IC5: Due to Lenz’s law there is a force opposing the motion of the wire // Upward force exerted on wire as the field is such to oppose the change that creates it
• IC6: Opposite, downward force on magnets, so balance reading increases
• // Newton’s 3rd law - downward force on magnets, so balance reading increases

The student uses a strong, cylindrical magnet to investigate Lenz’s law. The student records the time taken for the magnet to fall through two hollow tubes of copper, tube A and tube B. The two tubes have the same length and cross-sectional area. Tube B has a vertical slit cut into it, as shown *Discuss the differences in the time taken for the magnet to fall through each tube (6)

📚 Oct 2022

• IC1: Change in flux linkage as magnet falls (through each tube) Or (magnetic) field lines cut the metal
• IC2: EMF induced (in each tube)
• IC3: Tube(s) made of conducting material, so there is a current Or Tube provides a closed circuit, so there is a current
• IC4: Magnetic field associated with this current
• IC5: Upward force exerted on magnet as the field is such to oppose the change that creates Or Due to Lenz’s law there is a force opposing the motion of the magnet
• IC6: Magnet takes less time to fall through Tube B because the slit reduces the number of paths for current in the conductor

Explain why a current was produced in the aluminium plate as it passed between the poles of the magnet (2)

📚 Jun 2022

• induced (in plate)
• due to change of flux linkage Or due to cutting of lines of flux Or due to cutting of magnetic field lines
• (Leads to current in plate) as the plate provides a (full) conducting path

*Some electric motor designs rely on electromagnetic induction. A laboratory demonstration of the principle of an induction motor is shown. An aluminium disc is free to rotate and is initially stationary. A powerful magnet is moved around the disc in the direction of the arrow, without touching the disc. A student suggests that the disc will start to rotate as the magnet is moved and that the disc will rotate in the same direction as the movement of the magnet. Discuss this suggestion (6)

📚 Jan 2022

• There is a change in the magnetic flux (linkage with aluminium disc) Or disc is cutting magnetic field/flux
• is induced
• Leads to a current (in the disc) (accept eddy current)
• Force acts on the disc, as there is a current in a magnetic field (accept reference to motor effect, FLHR or F = BIl if current in disc has been mentioned) Or field due to current in disc interacting with field due to magnet to cause force on disc
• According to Lenz’s law Or the direction of e.m.f./current is such to oppose (the cause of) the change in flux
• The disc moves to reduce this change (the same direction as the magnet) so correct suggestion

Just before the carriage reaches the end of the ride it is slowed by an electromagnetic brake. Powerful magnets are attached to the track. An aluminium fin is attached to the carriage. The fin moves through a narrow gap between the magnets. Explain why the fin will leave the gap with a much slower speed than it entered the gap (5)

📚 Oct 2021

• There is a change in flux linkage of the magnetic field and the metal fin Or The fin cuts magnetic field/flux
• This induces an emf (across the fin)
• Current is produced in the fin (accept eddy current)
• Force acts on the fin, as there is a current in a magnetic field Or field due to current in fin interacts with field due to magnets to cause force on fin
• The force opposes the motion due to Lenz’s law Or Energy dissipated by current comes from (reduction in) kinetic energy of vehicle

A student carried out an investigation of Lenz’s law. A copper tube was suspended from a force meter, as shown. A magnet was released at the top of the tube. When the magnet was falling through the tube, there was an increased reading on the force meter. *Explain why there was an increased reading on the force meter (6)

📚 Jun 2021

• change of flux linked to surrounding metal Or change of flux linked to copper tube
• e.m.f induced
• full conducting path available, so current in metal
• current produces magnetic field
• (by Lenz’s law the) magnetic field (due to the induced current) produces a force (on the magnet) that opposes the motion of magnet causing it
• upward force on magnet, so (increased) downward force on tube

Explain how steadily increasing the current in the central coil produces a current in the plasma (4)

📚 Jan 2021

• Varying current, so varying magnetic field
• Change in flux linkage with plasma (loop) Or magnetic field lines cut plasma (loop)
• Emf induced
• Plasma makes a complete circuit, so current (in plasma)

*Explain how applying a p.d. across the input coil causes the capacitor to charge (6)

📚 Oct 2020

• produces) alternating current in input coil
• (Alternating/varying current produces) a varying magnetic field in core Or (Alternating/varying current produces) a varying magnetic field in second coil
• There is a change in magnetic flux linkage with (second) coil
• induced
• Complete circuit, so current in capacitor circuit
• Diode produces direct current

The handle is used to rotate the coil between the magnetic poles. When a LED is connected across the coil, the LED flashes on and off as the coil rotates Explain this observation (4)

📚 Jan 2020

• (rotating coil in field causes) changing (magnetic) flux linkage with coil // wires/coils cut lines of (magnetic) flux
• Emf induced
• Complete circuit, so current in circuit
• Pd / current produces changes in direction (as opposite parts of the coil switch sides), so LED only shines when current is flowing in one direction

Conditions of electromagnetic induction

Explain why the egg cooks only where it is in contact with the pan (2)

📚 Jan 2024

• Only pan is heated // Surface of cooker does not get hot // Egg is not a conductor
• As current can only circulate in a conductor // there is no current in the surface // there is a current in the pan because it is a conductor

Lenz's law

Explain the direction of the induced emf (3)

📚 Oct 2023

• is such as to oppose the change that produces it
• (With a current) there would be a force to the right (opposing the motion)
• // There would be a force in the direction opposite to the motion
• is from P to Q

The student states that the current at X is into the page. Deduce whether the students’ statement is correct (4) You should refer to Lenz’s law.

📚 Jun 2023

• By Lenz’s law, current/e.m.f./field/force produced is so as to oppose the cause of the current/e.m.f.
• Force on wire due to interaction of induced current and field
• Force to left, so, by (Fleming) LHR...
• current into page and student is correct (dependent on MP3)

Explain the direction of the magnetic field (2)

📚 Oct 2022

• The direction of electric force will be downwards so magnetic force must be upwards
• and the magnetic field is into the page

Tracks of charged particles

Explain why the conducting sphere oscillates between the two places (3)

📚 Oct 2023

• When the sphere touches the plate it is charged with the same polarity
• The force on the sphere due to the electric field is away from that plate so it moves towards the opposite plate // the sphere is repelled from the plate with the charge of the same sign // the sphere is attracted towards the plate with opposite charge
• When the sphere touches the charged plate opposite the first it becomes oppositely charged and is repelled from that charged plate (and so on)
• // When the sphere touches the oppositely charged plate it becomes oppositely charged and is attracted to the first plate (and so on)

Explain why the conducting sphere starts to move between the bells during an electrical storm (2)

📚 Oct 2023

• (The bell connected to the lightning conductor (right) becomes positively charged so) electrons are attracted to the right-hand side of the sphere
• The sphere is attracted to the positively charged bell

Explain why electrons are deflected into a parabolic path when a potential difference is applied between A and B (3)

📚 Oct 2023

• There is a (resultant) force on the electrons in the vertical direction
• So the electrons are accelerated vertically
• But in the horizontal direction the electrons have a constant speed

Equipotential

Equipotential of a point charge (2)

📚 Jan 2023

Resistor-Capacitor circuit

The student planned to use the circuit to measure the potential difference V across the capacitor C as it was charged and discharged through the resistor R (2) GV 2 reasons why the circuit did not operate as intended

📚 Jan 2023

• When charging voltmeter is not across C, // When switch at X, voltmeter is not across C,
• When discharging the resistor isn’t in the circuit, // with switch at Y, the resistor isn’t in the circuit

Explain how the current on ammeter A2 would vary over the same time interval (2)

📚 Jan 2022

• The current would vary with time in the same way as on ammeter A1
• Because (current is same everywhere) in a series circuit

Explain how this circuit can maintain power to the electronic controller if the switch is opened for a short time. (3)

📚 Oct 2021

• The capacitor stores charge/energy
• (if the switch is open) the capacitor discharges through resistor/controller Or (if the switch is open) the p.d across the resistor/controller is maintained by the capacitor
• across capacitor will remain high enough to operate the controller for a short time Or current in circuit will remain high enough to operate the controller for a short time Or charge/energy stored is limited and will only last for a short time

Capacitance curves

Explain how the potential difference \(V_R\) across the resistor varies with time after the switch is closed (2)

📚 Jun 2022

• Either
• would decrease exponentially from 5 V
• would decrease exponentially to 0 V
• Because the sum of the p.ds across the capacitor and resistor must always add up to the supply p.d.
• across resistor must decrease from 5 V. so current in resistor decreases so rate of change of p.d. decreases

Magnetic force

The kinetic energy of the vehicle decreased as the aluminium plate moved between the poles of the manget. Explain why (2)

📚 Jun 2022

• Current carrying conductor within a magnetic field experiences a force
• Force opposite to direction of motion due to Lenz’s law (so kinetic energy is reduced) Or Energy dissipated by current (in plate) (according to \(P = I^2R\))
• Energy is conserved (so kinetic energy decreases)

Conservation laws

State 2 ways in which the diagram shows that an anti-muon must also have a positive charge (2)

📚 Oct 2021

• (to conserve charge, as) no other charged particle is produced Or no other track is produced
• It has the same direction of curvature (as the pion track)

Electric field line

A textbook states, an electric field line shows the path a free positive test charge follows. Discuss the accuracy of this statement for free positive test charges placed at point A and point B (4)

📚 Jun 2021

• Field lines show direction of force on a (positive) charge
• (So) field line shows the direction of acceleration
• Point A - Where the line is straight, a charge (initially at rest) will follow the line, so true in this case
• Point B - Curved line means acceleration always changing direction but velocity is not in the direction of acceleration so statement not true

Spiral track

Deduce the direction of the magnetic field (3)

📚 Jun 2021

• Curvature more in top half of picture
• Particle moving slower after passing through lead plate because energy lost, so moving from lower half to top half
• (Applying FLHR,) field into page

Thermionic emission

NAME & DSCBE the process in which electrons are produced by the filament (2)

📚 Oct 2020

• Thermionic emission
• Electrons in the heated metal gain energy and leave the surface

Electric field

State, with a reason, the polarity of the charge on the strands of web

📚 Jan 2020

• Negative because the direction of field is direction of force on a positive charge
• // field downwards means negatively charged earth and negative repels negative
• // negative because the force is in the opposite direction to the electric field

Capacitor

A student states: “a capacitor is being used in this circuit. The function of the capacitor is to store electric charge.” Explain why this is not a complete description of the function of a capacitor (3)

📚 Jan 2020

• The capacitor is an energy store
• The overall charge on the capacitor is zero
• The capacitor separates charge

4.3 Further Mechanics

Centripetal force explanation

ASSESS the claim made by passenger. (4) “When the car was travelling at high speed around the circular path, I was thrown outwards due to a force acting on me. The outward force acting on me was the centrifugal force.”

📚 Oct 2023

• if no force the car/passenger would continue in a straight line // a force is required to change direction for the car/passenger
• A force was exerted on the car/passenger towards the centre of the circle // an inwards force was exerted on the car/passenger at right angles to the motion // a centripetal force was exerted on the car/passenger
• The inward force is exerted by the car on the passenger
• There is no outward force (on the passenger) so the passenger’s claim is incorrect

Student A suggests that if the radius of the canopy was increased and rotated at the same angular velocity as before, the wires supporting the aeroplanes could be vertical. Student B suggests that the wires would be at an angle of greater than 19 degrees to the vertical. Explain whether either of the students is correct (5)

📚 Oct 2020

• If vertical, zero horizontal component Or must be at an angle for a horizontal component
• Must have resultant horizontal component for circular motion,so first student incorrect
• If at an angle the radius is greater than before
• Since ω the same and r increased, \(F = mrω^2\) increased Or Since ω the same and r increased, v must increase, so \(F = \frac{mv^2}{r}\) increased
• Component of tension must be greater so a greater angle is required and the second student is correct

Centripetal force at different positions

*The magnitude of the force exerted by the ball on the car was greatest at 0.04s and least at 0.12s (6) Discuss the position of the car at these two times You should consider the forces acting on the car You do not need to do any further calculations

📚 Jun 2023

• IC1: Magnitude of centripetal force is constant since speed is constant
• IC2: Centripetal force on car at bottom is normal contact force minus weight (F = N – W or N = F + W)
• IC3: When car is at bottom force is maximum
• IC4: Centripetal force on car at top is normal contact force plus weight (F = N + W (same direction) or N = F – W)
• IC5: When car is at top force is minimum
• IC6: At 0.04 s it is at the bottom and at 0.12 s it’s at the top

The child comments that as the ball goes round the circle with a constant speed, the size of the force on his hand changes. Discuss whether this comment is correct (4)

📚 Jan 2022

• Tension in cord is force on hand
• Centripetal force is constant
• Weight of ball is added to tension at top
• Weight is subtracted from tension at bottom so force on hand varies and child correct

Conservation of momentum

State the principle of conservation of momentum (2)

📚 Jan 2023

• Total momentum before an interaction = total momentum after interaction
• If no (external) unbalanced / resultant force acts // in a closed system

For this situation, a scaled vector diagram showing the velocities of the balls can be used to demonstrate the law of conservation of momentum. Explain why (2)

📚 Jun 2022

• (p = mv and mass of the balls is the same) so velocity (to scale) is proportional to momentum Or (conservation of momentum) (vector) sum of momentum after collision = momentum before collision
• Velocities (drawn to scale) will form a triangle Or (a scaled vector diagram can show) (vector) sum of velocity after collision = velocity before collision

Arise of circular motion

Explain how banking allows the aeroplane to fly in a horizontal circular path (4)

📚 Oct 2022

• Idea that vertical component of lift force equals weight of aeroplane
• Vertical component of resultant force is zero, so aeroplane does not accelerate vertically Or Vertical component of resultant force is zero so it would remain flying horizontally
• Horizontal component of lift force acts as centripetal force Or Resultant force on aeroplane is horizontal and acts as centripetal force Or Horizontal component of lift force acts at 90° to motion
• So it follows a circular path (dependent on MP3)

Explain why the sphere moves with circular motion (2)

📚 Jun 2022

• There is a resultant force due to tension and weight
• Resultant force is at 90\(^o\) to the motion of the hammer

\(r=\frac{mv}{bq}\)

After passing through the velocity selector, a beam of oxygen ions with the same velocity enters a region of uniform magnetic flux density. Different isotopes of oxygen can be present in the beam. Explain why the detector will only detect one particular isotope (3)

📚 Oct 2022

• Isotopes have different masses
• The magnetic force will be the same because charge is the same Or r = mv / Bq and B, q, v are all the same
• Different mass will lead to a circle/path with different radius/deflection (so only one isotope is detected)

Collision of particle

In some experiments, a high-energy electron collides with a stationary atom. In other experiment beams of high-energy electrons, travelling in opposite directions, collide head-on. New particles can be created from collisions Deduce which type of collision is more likely to produce new particles with the largest mass (3)

📚 Jun 2022

• Reference to \(E=mc^{2}\)
• There will be more kinetic energy available (for the same accelerating p.d.) with colliding beams
• (Total) momentum of two beams is zero before collision
• Or single beam and stationary target has (net) momentum before collision
• AND
• All of the kinetic energy of the two beams available (to be converted to mass) so colliding beams more likely to produce particle with larger mass
• Or
• So with single beam particle(s) must have momentum after collision so less energy available (to be converted to mass) so lower mass particles produced
• Or So with single beam particle(s) must have kinetic energy after collision so less energy available (to be converted to mass) so lower mass particles produced

Derive \(a = rω^2\)

Derive centripetal acceleration

📚 Jan 2022

• [there is supposed to be a pic]

Resistor-Capacitor circuit

Add to the diagram to show a suitable circuit for charging and discharging the capacitor while measuring the p.d. across it (3)

📚 Jun 2021

• Battery in series with capacitor and resistor
• Voltmeter/datalogger/oscilloscope in parallel with capacitor
• Appropriate switching mechanism and discharge circuit
• [there is supposed to be a picture here]

Conservation laws

A stationary anti-neutron decays by emitting a positron. Explain how energy is conserved in this decay (2)

📚 Jan 2021

• Mass of products is less than mass of antineutron Or particles have kinetic energy after decay
• Where mass difference and the kinetic energy are related by \(∆E = c^2∆m\)

Miscellaneous

1.3 Mechanics

Explain what will happen to the vertical motion of the aeroplane (2)

📚 Jan 2023

• Resultant upwards force // lift is greater than weight // vertical component of lift is now greater than weight
• Aeroplane will accelerate upwards

2.3 Waves and Particle Nature of Light

Thomsons’s son directed beams of electrons at thin films of metal. The photograph shows one of the patterns observed Explain how this pattern changed scientists’ understanding about the nature of electrons (3)

📚 Jan 2023

• This is a diffraction/interference pattern
• Diffraction ONLY occurs for waves // Particles do not undergo diffraction
• (So) an electron does not always behave as a particle // (so) electrons can behave as waves (and as particles)

Resistance

Suggest why the percentage reduction in kinetic energy increases as the thickness of the plate increases (3)

📚 Jun 2022

• Reference to R = ρl/A Or refers to resistance of plate decreasing with increasing thickness/CSA
• So current will increase (as induced emf will be the same)
• So rate of energy transferred to surroundings increased Or larger braking force

Mechanics

Explain how this enables the helicopter to maintain a constant height above the ground (4)

📚 Jan 2022

• The blades exert a downward force on the air
• The air exerts an equal upwards force on the blades/helicopter Or By Newton’s 3rd law there is an equal upwards force
• This upwards force equals the weight of helicopter
• The resultant force is zero, so (by Newton’s 1st or 2nd law) there is no acceleration (and the helicopter maintains a constant height)

Stationary waves

Explain how standing waves are produced (3)

📚 Oct 2020

• Waves travelling in opposite direction (meet and) superpose/interfere Or a wave and a reflected wave (meet and) superpose/interfere
• At points where waves in antiphase destructive interference takes place Or At points where waves in phase constructive interference takes place
• Zero/minimum amplitude at points where destructive interference takes place Or Maximum amplitude at points where constructive interference takes place Or Nodes at points where destructive interference takes place Or Antinodes at points where constructive interference takes place

Suggest whether there are many significant advantages that would justify the cost (2)

📚 Jan 2020

• Higher speeds can be used
• A smaller track can be used
• The kart is less likely to skid
• The (maximum) centripetal force is larger

4.5 Nuclear and Particle Physics

Tracks of charged particles

A charged particle interacts with a stationary proton at P. This produces two neutral particles. Each of these neutral particles is unstable and decays into other particles. Explain the evidence provided by the diagram for this description of the particle interactions (3)

📚 Jan 2024

• There are no tracks after P
• (Only) charged particles leave tracks // Uncharged /neutral particles leave no tracks
• ‘V’ points on photograph identified as subsequent decays

State 2 ways that the diagram shows the kaon is neutral

📚 Jun 2022

• Kaon does not leave a track
• Pions have opposite charge and charge is conserved

Explain the process that enables a particle detector to detect charged particles (2)

📚 Jan 2022

• (the particle is) ionising Or it knocks electrons out of atoms in its path
• A track is formed by the ionised particles produced

Explain whether the maximum acceleration would be the same as for the alpha particle reflected back through 180 degree (4)

📚 Jan 2021

• alpha particle does not ever have zero speed/ke
• so not all of the energy has been transferred from the kinetic energy store to the electric potential energy store
• it is not as close to the nucleus Or minimum r is greater
• so (max) force is less, so (max) acceleration is less

Alpha particle scattering experiment

The interaction at P is neutral DSCBE the observations from these experiments and the conclusions that were made from these observations (5)

📚 Jan 2024

• Most alphas went straight through // Most alpha particles were undeviated
• So atom is mainly empty (space) (MP2 dependent on MP1)
• A few alpha particles were deflected by small angles
• very few alpha particles had a deflection > 90° // Very few alpha particles came straight back
• There is a concentration of charge in the atom (MP5 dependent on MP3 or MP4) // There is a concentration of mass in the atom

State 3 observations and the corresponding conclusions made from the alpha particle scattering experiment (6)

📚 Jun 2022

• Most alpha particles were undeviated Or Most particles pass through with little or no deviation
• Most of the atom is empty space (MP2 with reference to lack of deviation)
• Few alpha particles were scattered by small angles
• There is a concentration of charge in the atom (MP4 with reference to scattering)
• Very few alpha particles were deviated by more than 90°
• Most of the mass is concentrated in a small region of the atom
• Or Most of the mass is concentrated in nucleus (Accept Mass of nucleus much greater than mass of alpha particle) (MP6 with reference to back scattering)

*Following these experiments Rutherord said, “it was almost as incredible as if you fired a 12-inch shell (large missile) at a piece of tissue paper and it came back and hit you.” Explain why Rutherford was surprised at the results of the experiment and how this led to the nuclear model for the atom (6)

📚 Oct 2021

• IC1 plum pudding model of atom prior to experiment Or J J Thomson model of atom prior to experiment Or atom believed to have an equally distributed mass/charge throughout
• IC2 alpha particles expected to go straight through Or alpha particles expected to have only a small deflection
• IC3 a small number of alphas deflected through very large angles Or a small proportion of alphas come straight back
• IC4 (changed to) model of the atom having very small nucleus Or (changed to) model of atom where most is empty space
• IC5 nucleus contains (almost) all the mass
• IC6 nucleus is charged

Explain why the thickness of the gold foil had to be very small (2)

📚 Oct 2021

• Either
• a thin sheet would contain few layers of atoms
• so alpha particles would be less likely to undergo multiple deflections Or so alpha particles would be less likely to be absorbed
• OR
• alpha particles are strongly ionising
• so alpha particles can only penetrate a thin sheet or so alpha particles have low penetration

Explain how the results of the experiment led to this conclusion (atom has central charge contained in a very small volume) (2)

📚 Oct 2020

• Only a few particles were deflected
• So only a few came close enough to be deflected (so the charge must occupy a small volume)

Rutherford wrote, “the main deductions from the theory are independent of whether the central charge is positive or negative.” Discuss why the observations did not allow Rutherford to conclude whether the central charge is positive or negative (4) You may wish to use diagrams to illustrate your response.

📚 Oct 2020

• Alpha particles close to a –ve nucleus would experience a force towards it and be deviated slightly (ii)
• Alpha particles close to a +ve nucleus would experience a force away from it and be deviated slightly (v)
• Alpha particles very close to a –ve nucleus would experience a force towards it and be deviated right around it and back again (iii)
• Alpha particles approaching a +ve nucleus directly would experience a force away from it and be deviated right back again (vi)
• All of the possible observed paths can be explained by both types of nucleus, so the suggestion is correct

State why the alpha source and gold foil were contained in a vacuum (1)

📚 Jan 2020

• So no collisions with air molecules // so the air doesn’t stop alpha particles from reaching the detector

Discuss the extent to which the results of the alpha particle scattering experiments justified replacing the plum pudding model with a nuclear model of the atom (6)

📚 Jan 2020

• Most alpha particles passed straight through the gold foil
• Some alpha particles were deflected by small angles
• Either model would predict small or zero deflections because in the nuclear model the atom is mostly empty space and in the ‘pudding’ model matter is too spread out
• A few proportion of alpha particles were deflected by more than 90d
• This did not fit the plum pudding model as this deflection requires a high concentration of charge (to provide a large force) // this can only be explained by the nuclear model as this deflection requires a high concentration of charge to (produce a large force)
• This did not fit the plum pudding model as this deflection requires a high concentration of mass // this could only be explained by the nuclear model as this deflection requires a high concentration of mass (so that the alpha particle is deflected and not the gold nucleus)

Deduce quark structure

Explain the quark structure of a K- meson (2)

📚 Jan 2024

• s u̅
• The meson must be a quark-antiquark pair and include a strange quark
• // The meson must be a quark-antiquark pair and have a charge of −1

How a cyclotron works

Explain how the cyclotron produces a beam of high energy particles (4) Refer to the alternating potential difference and 2) the magnetic field

📚 Jan 2024

• accelerates particles
• gives particles energy
• Magnetic field / force at right angles to particles path
• Magnetic field/force maintains circular motion (whilst in dees)
• // Particle experiences centripetal force / acceleration (whilst in dees)
• switches every half cycle
• // Polarity of dees switches every half cycle
• switches when particle is in dees
• has a constant time period
• has a constant frequency
• // period is independent of speed of particle

Explain why a magnetic field is applied at right angles to the dees in the cyclotron (2)

📚 Jun 2023

• The particles experience a force at right angles to their motion/path/velocity.
• Which causes centripetal acceleration/force // Which causes circular motion

*Explain the role of electric and magnetic fields in the production of high-speed charged particles by a cyclotron (6)

📚 Jan 2021

• Magnetic field perpendicular to velocity of particles
• Magnetic force on particles perpendicular to velocity
• Particles experience centripetal acceleration/force so they undergo circular motion
• Alternating potential difference between dees changes direction while particle in dees
• Particle accelerated by electric field between dees
• (Electric) field in correct direction so that force on particle further increases speed

Explain the significance of the expression obtained by Lawrence to the operation of a cyclotron (4)

📚 Jan 2020

• Time independent of speed // radius
• So particles take constant time to complete circular path // particles spend the same time in each dee
• So a fixed frequency can be used for the pd
• / field across the gap will be in the correct direction to increase the speed the speed of the particles as they cross each time

Conservation laws

Explain 2 other conservation laws that apply to this decay (4)

📚 Oct 2023

• Any two pairs of:
• (Conservation of) charge
• −1 → −1 + 0
• (Conservation of) lepton number
• 0 → 1 + −1
• (Conservation of) baryon number
• 0 → 0 + 0

Explain whether the following decay would be possible (3)

📚 Jan 2023

• You should consider conservation of charge and lepton number
• Charge of particles shown: –1, –1, 0, 0
• Lepton number of particles shown: 1, 1 ,1, –1
• Charge conserved and lepton number conserved, so possible // But muon lepton number: 1 does not = –1, not obeyed, so not possible // But electron lepton number: 0 does not = 1+1, not obeyed, so not possible

Deduce the charge and the baryon number for the omega particle (3)

📚 Jan 2022

• applies charge conservation
• omega baryon charge −1
• baryon number: before = 1 identified as the proton so the omega particle = 1

*The rest mass of the omega baryon is significantly larger than the rest mass of the proton. Discuss how energy and momentum are conserved during this collision (6)

📚 Jan 2022

• Energy:
• IC1 As (Rest) mass-energy of proton and kaon + Initial \(E_k\) = (rest) mass-energy of omega and kaon + kinetic energies of both particles
• Or (Total) mass-energy conserved
• IC2 Incoming \(K^−\) had high kinetic energy
• IC3 some of this initial kinetic energy converted to mass of the omega particle (– mass of proton)
• IC4 \(∆E = ∆mc^2\)
• Momentum:
• IC5 momentum of \(K^−\) = sum of x components of \(K^+\) + \(Ω^−\)
• Or vector sum of momentum of \(K^+\) + \(Ω^−\) = momentum of \(K^−\)
• Or an attempt to sketch a triangle of vectors (be exact, give example)
• eg
• IC6 y component of \(K^+\) equals y component \(Ω^−\) Or all vectors correctly labelled

A student correctly suggests that this collision cannot lead to both particles being omega baryons, as this breaks a conservation law. Discuss the student’s suggestion (3)

📚 Oct 2021

• If both omega, it would break the conservation of baryon number
• Must be omega and anti-omega
• Further detail of baryon number: If both omega, before collision baryon number = 0 and after collision baryon number = 2 (which breaks conservation law) Or If omega and anti-omega before collision baryon number = 0 and after 1 – 1 = 0 (which obeys conservation law)

Explain how this equation shows that the decay obeys three conservation laws (6)

📚 Jan 2021

• Conservation of charge (because same before and after)
• Antineutron charge = 0; charge of antiproton = –1, positron = 1, neutrino = 0; total charge after = 0
• Conservation of baryon number (because same before and after)
• Antineutron baryon number = –1; Antiproton baryon number = –1, positron = 0, neutrino = 0, Total baryon number after =–1
• Conservation of lepton number (because same before and after)
• Antineutron lepton number = 0; Antiproton lepton number = 0, positron = –1, neutrino = 1, Total lepton number after = 0

Explain the assumption made when applying the principle of conservation of momentum to collisions (2)

📚 Jan 2021

• The assumption is that no (resultant) external forces act
• Because if external forces act there will be acceleration, so the final momentum will be different than otherwise Or if external forces act there will be an (additional) impulse, so the change in momentum will be different

Relativistic effects

Explain how the average lifetime of these high-energy pions compares with the lifetime of pions at rest (2)

📚 Oct 2023

• (When v = 0.99c) relativistic effects will be significant
• // (When v = 0.99c) time dilation occurs
• The lifetime (of high energy pions) would be longer (than for pions at rest)

Most types of quark form hadrons on a timescale of \(10^{-23}\)s. The top quark does not form hadrons because its lifetime is only \(10^{-25}\)s. A student suggests that, if the top quarks travelled at relativistic speeds, it could be possible for them to form hadrons. ASSESS this suggestion (2)

📚 Jan 2023

• (An observer will see an) increased lifetime
• But the time to form hadrons would also increase as seen by the observer, so it is incorrect // the lifetime would not increase as seen by the top quark, so it is incorrect

Z bosons produced by high energy collisions can have a range of lifetimes. The Z bosons with the longest lifetimes are those that were moving very fast. (2) Explain this observation.

📚 Oct 2022

• At speeds close to the speed of light
• There is a relativistic increase in lifetime Or time dilation occurs

Stationary muons are unstable and have a mean lifetime of a few microseconds. Explain why muons in the ring are observed to have a much greater mean lifetime. (2)

📚 Jan 2022

• muons travelling close to speed of light
• relativistic effect on particle lifetime

Most of the particles detected in the spark chamber are muons. The muons were created in the upper atmosphere. Muons normally have a very short lifetime and should have decayed before they reach the surface of the earth. Explain why these muons reach the surface of the earth (3)

📚 Oct 2021

• muons travelling close to speed of light
• relativistic effect increases particle lifetime (for observer)
• so travels further than normally expected (before decaying)

Explain whether these observations are consistent with ideas from relativity (5)

📚 Jan 2021

• The speed of the muon is very close to the speed of light
• Calculate distance travelled at 0.994 c in the average lifetime (without relativistic effects) = 656 m Or Calculate the time to travel 1600 m at 0.994c = 5.4 x 10-6 s
• Comparative comment about calculated value and situation if no relativistic effects
• Comment about lifetime linked to relativistic effects Or Comment about time of flight linked to relativistic effects
• Reason why most reach the ground

How a LINAC works

Explain the use of electric fields in a linac (4) Refer to the frequency of the a.c. supply

📚 Jun 2023

• The particles are accelerated by an electric field in the gaps
• frequency is constant so the particles spend the same time in the tubes/gaps
• (This is achieved by) increasing length of drift tubes // (This is achieved by) increasing length of gaps
• The (a.c) polarity changes so the (electric) field is in the same direction when the particle is in the gaps // The (a.c.) polarity changes so it is always accelerating the particles

*Explain why the distances between consecutive tubes increase in the first section of the linac but are almost equally spaced in the last section of the linac (6)

📚 Jun 2022

• ​​IC1 Electrons accelerate in the gaps
• supply is constant
• IC3 Time taken for an electron to travel between (consecutive) tubes is constant (and they are accelerating)
• electrons travel further in a fixed time with a higher speed
• IC5 (In the last section of the linac) the electron approaches the speed of light
• IC6 Speed becomes (almost) constant so distance travelled in a fixed amount of time becomes (almost) constant

Explain why the arrangement of linac works with a constant frequency a.c. supply (4)

📚 Oct 2021

• The beam/electron/positron is gaining speed
• The length of tubes increases or the length of gaps between tubes increases
• So time between beam exiting (successive) tubes is constant Or time spent in each tube is constant Or time spent between (each successive pair of) tubes is constant
• has to reverse in this time period and hence frequency is constant

For very high energy electrons, successive drift tubes have the same length. Explain why (2)

📚 Oct 2020

• As the electrons approach the speed of light there is no appreciable increase in speed
• v is constant and the electrons spend the same time in(/between) drift tubes, so s = vt must be constant

Standard quark-lepton model

Explain why the existence of a sixth quark was predicted (3)

📚 Jan 2023

• 1st generation, u and d, are a pair and 2nd generation, s and c, are a pair
• So 6th quark is a pair with b
• By symmetry of the standard model

DSCBE the structure of a baryon and a meson (2)

📚 Jan 2022

• A baryon is made of 3 quarks
• A meson is made of 1 quark & 1 antiquark

The muon belongs to the same family of particles as the electron. State how the muon is classified in the standard model (2)

📚 Jan 2022

• It is a lepton
• It is a fundamental particle Or second generation

State the properties of a positron that show it is the antiparticle to the electron (3)

📚 Jun 2021

• Mass equal (to mass of electron)
• Charge equal and opposite (to charge of electron)
• Lepton number (equal and) opposite (to lepton number of electron)

Explain why muons are not described as mesons in the standard model (2)

📚 Jan 2021

• Muons are leptons Or Muons are fundamental/elementary particles
• but mesons are made of quarks Or mesons are made of quark-antiquark

Compare this model with the current standard model (4)

📚 Oct 2020

• Similarities
• Zweig model, baryon 3 aces and standard model baryon 3 quarks, so similar
• Zweig model, meson 2 aces and standard model meson 2 quarks, so similar
• Zweig model, number of aces same as lepton and standard model quarks same as leptons, so similar
• Zweig model, aces have fractional charge and standard model quarks have fractional charge, so similar
• Zweig model, aces are fundamental and standard model quarks are fundamental, so similar
• Zweig model, aces have baryon number 1/3 and standard model quarks have baryon number 1/3, so similar
• Differences
• Zweig model, meson 2 aces but standard model meson quark antiquark, so different
• Zweig model, 4 aces in total but standard model 6 quarks in total, so different
• Zweig model, 4 leptons in total and standard model 6 leptons, so different
• Zweig model, no anti-aces but standard model has anti-quarks, so different

DSCBE how the underlined particles (electron, proton, neutron, meson, muon) fit into the standard model (6)

📚 Jan 2020

• Neutrons / protons are baryons
• baryons/ neutrons / protons made of 3 quarks
• Mesons made of quark and antiquark
• Electrons / muons are leptons
• p/n/e first generation // muon second generation
• Leptons / electron / muon / quarks fundamental // proton / neutron / mesons not fundamental

Collision of particle

Explain the advantage of colliding beams of particles (4)

📚 Jan 2023

• If target is stationary there is resultant momentum, so products must have resultant momentum after collision
• So products must have high kinetic energy
• (Therefore) less/little energy available for formation of particles
• (so) less massive particles formed
• OR
• If beams collide there is zero resultant momentum, so products may have no/low momentum after collision
• So products do not have high kinetic energy
• (Therefore) all/most/more energy available for formation of particles
• (so) more massive particles formed

Protons and anti-protons were accelerated in the Spp_barS to very high energies before they collided. (3) Explain why the protons and anti-protons needed high energies to produce the Z boson

📚 Oct 2022

• Mass-energy is conserved Or refers to \(ΔE = c^{2}Δm\)
• Need for large amounts of energy to create a high-mass particle Or Need more energy because mass of Z much greater than mass of proton(s) [accept 97 times]
• (Additional) energy comes from the kinetic energy of colliding particles

Explain why high energy particles are required to investigate the structure of the nucleons (3)

📚 Jan 2020

• High energy so particles have large momentum
• High momentum so that de Broglie wavelength is small
• Studying nucleons requires wavelengths of the order of nucleon size

Range and penetration of alpha, beta, gamma particles

Alpha particles were chosen by Rutherford for large-angle scattering experiments. Explain why alpha particles are more suitable for these experiments compared to beta particles or gamma rays (3)

📚 Oct 2022

• Alpha has double the charge (of beta)
• So for alpha deflecting force will be more (for same separation)
• Beta particles are much less massive than alpha particles
• So beta might be deflected by the electrons (surrounding the nucleus of gold)
• Gamma isn’t charged
• So gamma will not deflect at all (electrostatically) Or gamma will not experience any electrostatic force
• Gamma more penetrating
• So gamma less likely to interact

Spiral track

Explain how the diagram shows that the anti-muon is travelling in a clockwise path (3)

📚 Oct 2021

• The radius of the (spiral) path decreases (following it clockwise)
• The momentum/velocity/speed of the particle is decreasing
• as energy is transferred from the anti-muon (by ionisation and electromagnetic radiation)

Tracks of charged practicles

State a reason why radon atoms do not leave tracks (1)

📚 Oct 2020

• They are uncharged Or they do not cause ionisation

Deduce which track is for the first alpha particle emitted (3)

📚 Oct 2020

• There is a gap between the start of the two tracks
• The atom/ion/nucleus produced after alpha decay would recoil in the opposite direction before emitting the next alpha
• So we can tell that the track on the right was produced by the first alpha
• OR
• The track on the right is thicker (than the track on the left)
• This means that the track has had a longer time in which to disperse
• So we can tell that the track on the right was produced by the first alpha

4.4 Electric and Magnetic Fields

Data inferences

Explain how the time taken to charge the capacitor would change (3) You do not need to do any further calculations

📚 Jan 2024

• Resistance in circuit would decrease
• So current in circuit would increase // so time constant will decrease // so T = RC will decrease
• (Hence) capacitor would charge more quickly
• MP2 dependent on MP1, MP3 dependent on MP2

Explain the extent to which the students’ results support this statement (3)

📚 Jan 2021

• The maxima are integer multiples of \(1.6 × 10^{−19} C\) Or The peaks are at intervals of \(1.6 × 10^{−19} C\)
• The spread about the maxima is small
• This could be due to experimental error, so the statement is supported

Explain how the behaviour of the LED shown in the graph will affect the time taken for the light intensity to decrease to zero (3)

📚 Jan 2020

• From the graph, as pd decreases the resistance increases
• Therefore the time constant increases
• The light will take longer to switch off

Explain the changes in the graph when the angular velocity of the coil is halved (2)

📚 Jan 2020

• (Half angular velocity) so takes twice as long to turn, so period halved
• (Half angular velocity) so rate of change of flux halved so emf halved

Electromagnetic induction

*Explain why the kettle heats up when there is an alternating current in the coil (6)

📚 Jan 2024

• IC1 The current produces a magnetic field
• IC2 Alternating current, so alternating/varying magnetic field
• IC3 There is a change of flux linkage with kettle/core due to the
• alternating current // Lines of magnetic flux cut the kettle/core.
• is induced across the kettle/core
• IC5 Currents circulate in (the iron of) the kettle/core
• IC6 The kettle heats as energy is dissipated by the heating effect of currents // the core heats as energy is dissipated and the thermal energy is transferred to the kettle by conduction

A bar magnet was dropped vertically through a small coil. *Explain the variation of emf with time (6)

📚 Oct 2023

• IC1 There is a change in flux linkage (with the coil)
• // the wires cut the magnetic field (lines)
• IC2 The greater the RATE of change of flux linkage the larger the induced e.m.f.
• IC3 After the south pole REACHES the coil the flux linkage (starts to) decrease
• // When the south pole reaches the coil, by Lenz’s law the polarity of the coil changes to continue to resist the motion of the magnet
• // As the south pole reaches the coil the rate of change of flux linkage is zero
• is negative
• IC5 The (downwards) speed of the magnet increases
• IC6 Emf is zero before magnet enters coil
• // Emf is zero when midpoint of magnet in coil
• // Maximum negative value is greater than maximum positive value
• // Time for which emf is negative is greater than time for which emf is positive
• // emf is zero when magnet totally leaves coil

Explain why a p.d. was produced as the coil was rotated (2)

📚 Jun 2023

• (Wires) cut lines of magnetic FLUX // flux linkage (with coil) changing
• Induces emf

*When the student moved the wire quickly downwards between the magnets, the reading on the balance changed. Explain how the reading on the balance changed (6)

📚 Jan 2023

• IC1: Wire cuts lines of magnetic flux // Wire cuts magnetic field lines // flux linkage of wire changes
• IC2: Induces e.m.f.
• IC3: so current in loop of wire
• IC4: Current in a wire in a magnetic field experiences a force // Magnetic field associated with this current
• IC5: Due to Lenz’s law there is a force opposing the motion of the wire // Upward force exerted on wire as the field is such to oppose the change that creates it
• IC6: Opposite, downward force on magnets, so balance reading increases
• // Newton’s 3rd law - downward force on magnets, so balance reading increases

The student uses a strong, cylindrical magnet to investigate Lenz’s law. The student records the time taken for the magnet to fall through two hollow tubes of copper, tube A and tube B. The two tubes have the same length and cross-sectional area. Tube B has a vertical slit cut into it, as shown *Discuss the differences in the time taken for the magnet to fall through each tube (6)

📚 Oct 2022

• IC1: Change in flux linkage as magnet falls (through each tube) Or (magnetic) field lines cut the metal
• IC2: EMF induced (in each tube)
• IC3: Tube(s) made of conducting material, so there is a current Or Tube provides a closed circuit, so there is a current
• IC4: Magnetic field associated with this current
• IC5: Upward force exerted on magnet as the field is such to oppose the change that creates Or Due to Lenz’s law there is a force opposing the motion of the magnet
• IC6: Magnet takes less time to fall through Tube B because the slit reduces the number of paths for current in the conductor

Explain why a current was produced in the aluminium plate as it passed between the poles of the magnet (2)

📚 Jun 2022

• induced (in plate)
• due to change of flux linkage Or due to cutting of lines of flux Or due to cutting of magnetic field lines
• (Leads to current in plate) as the plate provides a (full) conducting path

*Some electric motor designs rely on electromagnetic induction. A laboratory demonstration of the principle of an induction motor is shown. An aluminium disc is free to rotate and is initially stationary. A powerful magnet is moved around the disc in the direction of the arrow, without touching the disc. A student suggests that the disc will start to rotate as the magnet is moved and that the disc will rotate in the same direction as the movement of the magnet. Discuss this suggestion (6)

📚 Jan 2022

• There is a change in the magnetic flux (linkage with aluminium disc) Or disc is cutting magnetic field/flux
• is induced
• Leads to a current (in the disc) (accept eddy current)
• Force acts on the disc, as there is a current in a magnetic field (accept reference to motor effect, FLHR or F = BIl if current in disc has been mentioned) Or field due to current in disc interacting with field due to magnet to cause force on disc
• According to Lenz’s law Or the direction of e.m.f./current is such to oppose (the cause of) the change in flux
• The disc moves to reduce this change (the same direction as the magnet) so correct suggestion

Just before the carriage reaches the end of the ride it is slowed by an electromagnetic brake. Powerful magnets are attached to the track. An aluminium fin is attached to the carriage. The fin moves through a narrow gap between the magnets. Explain why the fin will leave the gap with a much slower speed than it entered the gap (5)

📚 Oct 2021

• There is a change in flux linkage of the magnetic field and the metal fin Or The fin cuts magnetic field/flux
• This induces an emf (across the fin)
• Current is produced in the fin (accept eddy current)
• Force acts on the fin, as there is a current in a magnetic field Or field due to current in fin interacts with field due to magnets to cause force on fin
• The force opposes the motion due to Lenz’s law Or Energy dissipated by current comes from (reduction in) kinetic energy of vehicle

A student carried out an investigation of Lenz’s law. A copper tube was suspended from a force meter, as shown. A magnet was released at the top of the tube. When the magnet was falling through the tube, there was an increased reading on the force meter. *Explain why there was an increased reading on the force meter (6)

📚 Jun 2021

• change of flux linked to surrounding metal Or change of flux linked to copper tube
• e.m.f induced
• full conducting path available, so current in metal
• current produces magnetic field
• (by Lenz’s law the) magnetic field (due to the induced current) produces a force (on the magnet) that opposes the motion of magnet causing it
• upward force on magnet, so (increased) downward force on tube

Explain how steadily increasing the current in the central coil produces a current in the plasma (4)

📚 Jan 2021

• Varying current, so varying magnetic field
• Change in flux linkage with plasma (loop) Or magnetic field lines cut plasma (loop)
• Emf induced
• Plasma makes a complete circuit, so current (in plasma)

*Explain how applying a p.d. across the input coil causes the capacitor to charge (6)

📚 Oct 2020

• produces) alternating current in input coil
• (Alternating/varying current produces) a varying magnetic field in core Or (Alternating/varying current produces) a varying magnetic field in second coil
• There is a change in magnetic flux linkage with (second) coil
• induced
• Complete circuit, so current in capacitor circuit
• Diode produces direct current

The handle is used to rotate the coil between the magnetic poles. When a LED is connected across the coil, the LED flashes on and off as the coil rotates Explain this observation (4)

📚 Jan 2020

• (rotating coil in field causes) changing (magnetic) flux linkage with coil // wires/coils cut lines of (magnetic) flux
• Emf induced
• Complete circuit, so current in circuit
• Pd / current produces changes in direction (as opposite parts of the coil switch sides), so LED only shines when current is flowing in one direction

Conditions of electromagnetic induction

Explain why the egg cooks only where it is in contact with the pan (2)

📚 Jan 2024

• Only pan is heated // Surface of cooker does not get hot // Egg is not a conductor
• As current can only circulate in a conductor // there is no current in the surface // there is a current in the pan because it is a conductor

Lenz's law

Explain the direction of the induced emf (3)

📚 Oct 2023

• is such as to oppose the change that produces it
• (With a current) there would be a force to the right (opposing the motion)
• // There would be a force in the direction opposite to the motion
• is from P to Q

The student states that the current at X is into the page. Deduce whether the students’ statement is correct (4) You should refer to Lenz’s law.

📚 Jun 2023

• By Lenz’s law, current/e.m.f./field/force produced is so as to oppose the cause of the current/e.m.f.
• Force on wire due to interaction of induced current and field
• Force to left, so, by (Fleming) LHR...
• current into page and student is correct (dependent on MP3)

Explain the direction of the magnetic field (2)

📚 Oct 2022

• The direction of electric force will be downwards so magnetic force must be upwards
• and the magnetic field is into the page

Tracks of charged particles

Explain why the conducting sphere oscillates between the two places (3)

📚 Oct 2023

• When the sphere touches the plate it is charged with the same polarity
• The force on the sphere due to the electric field is away from that plate so it moves towards the opposite plate // the sphere is repelled from the plate with the charge of the same sign // the sphere is attracted towards the plate with opposite charge
• When the sphere touches the charged plate opposite the first it becomes oppositely charged and is repelled from that charged plate (and so on)
• // When the sphere touches the oppositely charged plate it becomes oppositely charged and is attracted to the first plate (and so on)

Explain why the conducting sphere starts to move between the bells during an electrical storm (2)

📚 Oct 2023

• (The bell connected to the lightning conductor (right) becomes positively charged so) electrons are attracted to the right-hand side of the sphere
• The sphere is attracted to the positively charged bell

Explain why electrons are deflected into a parabolic path when a potential difference is applied between A and B (3)

📚 Oct 2023

• There is a (resultant) force on the electrons in the vertical direction
• So the electrons are accelerated vertically
• But in the horizontal direction the electrons have a constant speed

Equipotential

Equipotential of a point charge (2)

📚 Jan 2023

Resistor-Capacitor circuit

The student planned to use the circuit to measure the potential difference V across the capacitor C as it was charged and discharged through the resistor R (2) GV 2 reasons why the circuit did not operate as intended

📚 Jan 2023

• When charging voltmeter is not across C, // When switch at X, voltmeter is not across C,
• When discharging the resistor isn’t in the circuit, // with switch at Y, the resistor isn’t in the circuit

Explain how the current on ammeter A2 would vary over the same time interval (2)

📚 Jan 2022

• The current would vary with time in the same way as on ammeter A1
• Because (current is same everywhere) in a series circuit

Explain how this circuit can maintain power to the electronic controller if the switch is opened for a short time. (3)

📚 Oct 2021

• The capacitor stores charge/energy
• (if the switch is open) the capacitor discharges through resistor/controller Or (if the switch is open) the p.d across the resistor/controller is maintained by the capacitor
• across capacitor will remain high enough to operate the controller for a short time Or current in circuit will remain high enough to operate the controller for a short time Or charge/energy stored is limited and will only last for a short time

Capacitance curves

Explain how the potential difference \(V_R\) across the resistor varies with time after the switch is closed (2)

📚 Jun 2022

• Either
• would decrease exponentially from 5 V
• would decrease exponentially to 0 V
• Because the sum of the p.ds across the capacitor and resistor must always add up to the supply p.d.
• across resistor must decrease from 5 V. so current in resistor decreases so rate of change of p.d. decreases

Magnetic force

The kinetic energy of the vehicle decreased as the aluminium plate moved between the poles of the manget. Explain why (2)

📚 Jun 2022

• Current carrying conductor within a magnetic field experiences a force
• Force opposite to direction of motion due to Lenz’s law (so kinetic energy is reduced) Or Energy dissipated by current (in plate) (according to \(P = I^2R\))
• Energy is conserved (so kinetic energy decreases)

Conservation laws

State 2 ways in which the diagram shows that an anti-muon must also have a positive charge (2)

📚 Oct 2021

• (to conserve charge, as) no other charged particle is produced Or no other track is produced
• It has the same direction of curvature (as the pion track)

Electric field line

A textbook states, an electric field line shows the path a free positive test charge follows. Discuss the accuracy of this statement for free positive test charges placed at point A and point B (4)

📚 Jun 2021

• Field lines show direction of force on a (positive) charge
• (So) field line shows the direction of acceleration
• Point A - Where the line is straight, a charge (initially at rest) will follow the line, so true in this case
• Point B - Curved line means acceleration always changing direction but velocity is not in the direction of acceleration so statement not true

Spiral track

Deduce the direction of the magnetic field (3)

📚 Jun 2021

• Curvature more in top half of picture
• Particle moving slower after passing through lead plate because energy lost, so moving from lower half to top half
• (Applying FLHR,) field into page

Thermionic emission

NAME & DSCBE the process in which electrons are produced by the filament (2)

📚 Oct 2020

• Thermionic emission
• Electrons in the heated metal gain energy and leave the surface

Electric field

State, with a reason, the polarity of the charge on the strands of web

📚 Jan 2020

• Negative because the direction of field is direction of force on a positive charge
• // field downwards means negatively charged earth and negative repels negative
• // negative because the force is in the opposite direction to the electric field

Capacitor

A student states: “a capacitor is being used in this circuit. The function of the capacitor is to store electric charge.” Explain why this is not a complete description of the function of a capacitor (3)

📚 Jan 2020

• The capacitor is an energy store
• The overall charge on the capacitor is zero
• The capacitor separates charge

4.3 Further Mechanics

Centripetal force explanation

ASSESS the claim made by passenger. (4) “When the car was travelling at high speed around the circular path, I was thrown outwards due to a force acting on me. The outward force acting on me was the centrifugal force.”

📚 Oct 2023

• if no force the car/passenger would continue in a straight line // a force is required to change direction for the car/passenger
• A force was exerted on the car/passenger towards the centre of the circle // an inwards force was exerted on the car/passenger at right angles to the motion // a centripetal force was exerted on the car/passenger
• The inward force is exerted by the car on the passenger
• There is no outward force (on the passenger) so the passenger’s claim is incorrect

Student A suggests that if the radius of the canopy was increased and rotated at the same angular velocity as before, the wires supporting the aeroplanes could be vertical. Student B suggests that the wires would be at an angle of greater than 19 degrees to the vertical. Explain whether either of the students is correct (5)

📚 Oct 2020

• If vertical, zero horizontal component Or must be at an angle for a horizontal component
• Must have resultant horizontal component for circular motion,so first student incorrect
• If at an angle the radius is greater than before
• Since ω the same and r increased, \(F = mrω^2\) increased Or Since ω the same and r increased, v must increase, so \(F = \frac{mv^2}{r}\) increased
• Component of tension must be greater so a greater angle is required and the second student is correct

Centripetal force at different positions

*The magnitude of the force exerted by the ball on the car was greatest at 0.04s and least at 0.12s (6) Discuss the position of the car at these two times You should consider the forces acting on the car You do not need to do any further calculations

📚 Jun 2023

• IC1: Magnitude of centripetal force is constant since speed is constant
• IC2: Centripetal force on car at bottom is normal contact force minus weight (F = N – W or N = F + W)
• IC3: When car is at bottom force is maximum
• IC4: Centripetal force on car at top is normal contact force plus weight (F = N + W (same direction) or N = F – W)
• IC5: When car is at top force is minimum
• IC6: At 0.04 s it is at the bottom and at 0.12 s it’s at the top

The child comments that as the ball goes round the circle with a constant speed, the size of the force on his hand changes. Discuss whether this comment is correct (4)

📚 Jan 2022

• Tension in cord is force on hand
• Centripetal force is constant
• Weight of ball is added to tension at top
• Weight is subtracted from tension at bottom so force on hand varies and child correct

Conservation of momentum

State the principle of conservation of momentum (2)

📚 Jan 2023

• Total momentum before an interaction = total momentum after interaction
• If no (external) unbalanced / resultant force acts // in a closed system

For this situation, a scaled vector diagram showing the velocities of the balls can be used to demonstrate the law of conservation of momentum. Explain why (2)

📚 Jun 2022

• (p = mv and mass of the balls is the same) so velocity (to scale) is proportional to momentum Or (conservation of momentum) (vector) sum of momentum after collision = momentum before collision
• Velocities (drawn to scale) will form a triangle Or (a scaled vector diagram can show) (vector) sum of velocity after collision = velocity before collision

Arise of circular motion

Explain how banking allows the aeroplane to fly in a horizontal circular path (4)

📚 Oct 2022

• Idea that vertical component of lift force equals weight of aeroplane
• Vertical component of resultant force is zero, so aeroplane does not accelerate vertically Or Vertical component of resultant force is zero so it would remain flying horizontally
• Horizontal component of lift force acts as centripetal force Or Resultant force on aeroplane is horizontal and acts as centripetal force Or Horizontal component of lift force acts at 90° to motion
• So it follows a circular path (dependent on MP3)

Explain why the sphere moves with circular motion (2)

📚 Jun 2022

• There is a resultant force due to tension and weight
• Resultant force is at 90\(^o\) to the motion of the hammer

\(r=\frac{mv}{bq}\)

After passing through the velocity selector, a beam of oxygen ions with the same velocity enters a region of uniform magnetic flux density. Different isotopes of oxygen can be present in the beam. Explain why the detector will only detect one particular isotope (3)

📚 Oct 2022

• Isotopes have different masses
• The magnetic force will be the same because charge is the same Or r = mv / Bq and B, q, v are all the same
• Different mass will lead to a circle/path with different radius/deflection (so only one isotope is detected)

Collision of particle

In some experiments, a high-energy electron collides with a stationary atom. In other experiment beams of high-energy electrons, travelling in opposite directions, collide head-on. New particles can be created from collisions Deduce which type of collision is more likely to produce new particles with the largest mass (3)

📚 Jun 2022

• Reference to \(E=mc^{2}\)
• There will be more kinetic energy available (for the same accelerating p.d.) with colliding beams
• (Total) momentum of two beams is zero before collision
• Or single beam and stationary target has (net) momentum before collision
• AND
• All of the kinetic energy of the two beams available (to be converted to mass) so colliding beams more likely to produce particle with larger mass
• Or
• So with single beam particle(s) must have momentum after collision so less energy available (to be converted to mass) so lower mass particles produced
• Or So with single beam particle(s) must have kinetic energy after collision so less energy available (to be converted to mass) so lower mass particles produced

Derive \(a = rω^2\)

Derive centripetal acceleration

📚 Jan 2022

• [there is supposed to be a pic]

Resistor-Capacitor circuit

Add to the diagram to show a suitable circuit for charging and discharging the capacitor while measuring the p.d. across it (3)

📚 Jun 2021

• Battery in series with capacitor and resistor
• Voltmeter/datalogger/oscilloscope in parallel with capacitor
• Appropriate switching mechanism and discharge circuit
• [there is supposed to be a picture here]

Conservation laws

A stationary anti-neutron decays by emitting a positron. Explain how energy is conserved in this decay (2)

📚 Jan 2021

• Mass of products is less than mass of antineutron Or particles have kinetic energy after decay
• Where mass difference and the kinetic energy are related by \(∆E = c^2∆m\)

Miscellaneous

1.3 Mechanics

Explain what will happen to the vertical motion of the aeroplane (2)

📚 Jan 2023

• Resultant upwards force // lift is greater than weight // vertical component of lift is now greater than weight
• Aeroplane will accelerate upwards

2.3 Waves and Particle Nature of Light

Thomsons’s son directed beams of electrons at thin films of metal. The photograph shows one of the patterns observed Explain how this pattern changed scientists’ understanding about the nature of electrons (3)

📚 Jan 2023

• This is a diffraction/interference pattern
• Diffraction ONLY occurs for waves // Particles do not undergo diffraction
• (So) an electron does not always behave as a particle // (so) electrons can behave as waves (and as particles)

Resistance

Suggest why the percentage reduction in kinetic energy increases as the thickness of the plate increases (3)

📚 Jun 2022

• Reference to R = ρl/A Or refers to resistance of plate decreasing with increasing thickness/CSA
• So current will increase (as induced emf will be the same)
• So rate of energy transferred to surroundings increased Or larger braking force

Mechanics

Explain how this enables the helicopter to maintain a constant height above the ground (4)

📚 Jan 2022

• The blades exert a downward force on the air
• The air exerts an equal upwards force on the blades/helicopter Or By Newton’s 3rd law there is an equal upwards force
• This upwards force equals the weight of helicopter
• The resultant force is zero, so (by Newton’s 1st or 2nd law) there is no acceleration (and the helicopter maintains a constant height)

Stationary waves

Explain how standing waves are produced (3)

📚 Oct 2020

• Waves travelling in opposite direction (meet and) superpose/interfere Or a wave and a reflected wave (meet and) superpose/interfere
• At points where waves in antiphase destructive interference takes place Or At points where waves in phase constructive interference takes place
• Zero/minimum amplitude at points where destructive interference takes place Or Maximum amplitude at points where constructive interference takes place Or Nodes at points where destructive interference takes place Or Antinodes at points where constructive interference takes place

Suggest whether there are many significant advantages that would justify the cost (2)

📚 Jan 2020

• Higher speeds can be used
• A smaller track can be used
• The kart is less likely to skid
• The (maximum) centripetal force is larger