Particles and radiation questions

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• AQA 7408 · June 2025 · Paper 1 · Q8 · 8 marks

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  Question 8.1 was answered correctly by 64% of students. Surprisingly about 8% did not attempt this calculation. Several careless mathematical or substitution errors were seen. Answers to Question 8.2 were often vague or based on the electrons starting with different speeds. The best answers made it clear that the kinetic energy of electrons was transferred to the gas atoms, or that the collisions were inelastic. Simply stating that collisions occurred was not enough. Question 8.3 also proved to be very difficult. Few students applied their knowledge of how fluorescent tubes work to the information in the question. Successful answers identified the peak in Figure 12 to be in the ultraviolet region and then went on to describe how this can be used by the phosphor in the coating to produce white light. More than 70% of students obtained all three marks for Question 8.4. Common errors included misreading the graph, not converting nm to m correctly and failing to convert to eV. The final mark was withheld from students who gave the answer ‘5’ as this is a 1sf answer. © 2025 AQA Section B The most straightforward multiple-choice questions were B11 and B13. Both were answered correctly by more than 90% of students. Several questions had discriminators more popular than the correct answer. The correct answer to B21 was the least popular. Most chose C, demonstrating that they did not understand that Newton’s third law pairs have to be the same type of force and act on different objects. Option B was the next most popular, chosen by students who did not understand that at terminal velocity the drag force is equal to the weight. 17% of students chose option A, perhaps due to the videos of skydivers where the camera continues to fall rapidly while the skydiver slows down after opening their parachute. The correct answer to B16 was the third most popular. Half of the students chose B. This is due to a common misconception about the resistance of a non-ohmic device. The next most popular was D. Students should be taught that it is the instantaneous values of current and voltage that are used to determine the resistance and power dissipated. The correct answer to B14 was the second most popular chosen by less than 20% of students. Almost 60% chose D. These students were confused between square roots and squares perhaps. This was a demanding question that rewarded students who knew which equations to use and were capable of doing the necessary algebra. The correct answer to B28 was the second most popular. 43% of the students chose B, suggesting that the current did not change, despite the circuit resistance being less.

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  Electrons in a fluorescent tube are accelerated from rest through a potential difference of 130 V.

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• AQA 7408 · June 2024 · Paper 1 · Q1 · 7 marks

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  More than 75% of students were able to answer question 01.1 correctly. The most common error was to write ‘electrostatic’ for ‘electromagnetic’. Question 01.2 was similarly well answered. There were many variations seen for the electron antineutrino. Care needs to be taken when writing the symbol to ensure that the subscript ‘e’ is not the same size as the n. In question 01.3, most students were able to identify the weak interaction as the one responsible for neutron decay. Many failed to obtain the second mark by giving weak or irrelevant answers. The best answers made a clear reference to leptons or the change in quark flavour. The most common mark awarded in question 01.4 was for identifying the virtual photon as the exchange particle. Very few students went on to explain the change in paths in terms of conservation of momentum. This is clearly a part of the specification that is poorly understood. The question did discriminate quite well, however.

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  This question is about fundamental interactions and the decay of a free neutron.

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• AQA 7408 · June 2024 · Paper 1 · Q2 · 9 marks

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  This was a particle-physics question set in the context of a pion–neutron interaction. More than half of students obtained both marks for question 02.1. A common error was only putting one tick in each row. These students presumably did not realise that a particle could be both a hadron and a meson, for example. The command sentence makes it clear that multiple boxes should be ticked for each particle. Students should be encouraged to read these command sentences carefully so that they understand what they need to do. Question 02.2 produced a good spread of marks and discriminated reasonably well. Most students identified conservation of strangeness as the rule being broken. Far fewer could explain their answer in sufficient clarity or detail. Many students referred to both weak and strong interactions in their answer, and therefore did not apply the conservation rule precisely to this situation. Question 02.3 required students to look up data in the data and formulae booklet and most managed to do this. Problems arose with the rest mass of the photon. Many students identified the difference in rest mass between the pion and positron/electron pair and assumed it was ‘given’ to the photon. The best answers made it clear that the photon rest mass is zero and that the difference in rest masses would be seen in the kinetic energies of the products. Surprisingly fewer than 35% of students identified annihilation of the positron with an electron as the source of more gamma photons in question 02.4. Question 02.5 tests a very small part of the specification that appears to be often overlooked. As a similar question had been asked on a previous series, it was expected that this would answer quite well. Just under 50% of students were awarded the mark. The most common answer that was not rewarded was a vague comment about peer review.

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  A positive pion collides with a neutron and produces a positive kaon and a neutral sigma particle: pi+ + n -> K+ + Sigma0. The strangeness of Sigma0 is -1.

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• AQA 7408 · June 2022 · Paper 1 · Q1 · 12 marks

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  Most students achieved both marks on 01.1. Students who wrote ‘a’ for the alpha particle did not receive credit. Several students also included other particles, such as neutrinos, in the equation. 01.2 proved to be much more challenging. Most students were able to access the first mark, but few went on to explain fully why the boson was the W–, often missing out any consideration of the significance of the charge. 01.3 required students to set out the evidence clearly, linking it to the particular element being discussed. Although it was not penalised, many students discussed whether the lines of hydrogen or sodium matched those of helium, rather than the other way around. Both 01.4 and 01.5 discriminated reasonably well, each producing a spread of marks. The calculation in 01.4 was correctly completed by most students. In a significant number of wrong answers there was an attempt to calculate an energy difference which lost credit. Answers that were based on a difference in wavelengths were penalised further. 01.5 proved to be more challenging. Answers were often vague or ambiguous. Important details related to the role of the photon, or the significance of energy levels, were also often missing. Rather than simply explaining emission, several students explained how the excitation happened in the first place, and this often led to confusion.

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  Two stable helium isotopes are ^4_2He and ^3_2He. The questions concern nuclear decay and atomic spectra. Helium absorption lines A-F occur at approximately 390, 440, 490, 505, 590 and 670 nm; line C coincides with hydrogen, line E coincides with sodium, and line D coincides with neither.

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• AQA 7408 · June 2022 · Paper 1 · Q2 · 7 marks

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  02.1 and 02.3 were answered correctly by the vast majority of students. Most students found 02.2 very challenging. An important aspect of the question was that there was a fixed amount of energy released in the process; this point was often missed. The confusion in many answers demonstrated that few students understood what the graph was telling them. 02.4 produced a good spread of marks and discriminated very well. Most students were able to pick up one mark for the energy calculation. Fewer went on to work out explicitly the energy of one photon. Fewer still saw that this was a minimum energy as it assumed that the particles were stationary.

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  Carbon-14 undergoes beta-minus decay to nitrogen-14, emitting an electron and an electron antineutrino. The beta particles have a continuous kinetic-energy distribution from near zero to a fixed maximum. In a separate reaction an electron antineutrino interacts with a proton: anti-nu_e + p -> e^+ + X.

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• AQA 7408 · November 2021 · Paper 1 · Q1 · 12 marks

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  Question 01.1 was answered correctly by a majority of students. However, although a mark was available for answers that included the calculation of the number of nucleons, this mark was withheld when the student made any suggestion that what they had calculated was the number of neutrons. This resulted in very few students receiving more than one out of three marks for partial answers. In question 01.2 many students were familiar with the kinetic energy equation, but had difficulties with the conversion between MeV and J. Answers to the remaining parts indicated that many students were unfamiliar with the conservation laws or the decay of the kaon into pions, which are both explicitly on the specification.

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  Cosmic-ray nucleus X has mass 8.02 x 10^-26 kg, specific charge 4.39 x 10^7 C kg^-1 and kinetic energy 215 MeV.

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• AQA 7408 · November 2021 · Paper 3A · Q2 · 10 marks

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  This question was about the light emitted from different LEDs but included general ideas about the use of diffraction gratings, as used in Required Practical Activity 2. In question 02.1 students had to make an easy read-off from Figure 3 and then apply an equation available in the Formulae and Data booklet. Despite the low demand of the question, fewer than a third of the students were able to obtain full credit. Question 02.2 is one of several in the paper where those suggesting simple practically-based explanations were most likely to score. About 40% of students mentioned some relevant characteristic of the 5th maximum to score the available mark. It was clear that some did not understand what we wanted them to do in question 02.3 and many showed no evidence of working on Figure 4. In question 02.4 only 3% of the students successfully used data about both LEDs; some engineered an answer that duplicated the value in the Formulae and Data booklet. All students realised that c is the speed of light but not all recognised that e is the electronic charge and used 2.718 in their calculation. Question 02.5 was the least accessible part and only 10% of students used Figure 4 to determine the voltage drop across the LED before going on to deduce the minimum value of R.

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  Green LED LG and red LED LR have equal peak intensity. Their spectral peaks are about 565 nm and 635 nm. Extrapolated activation voltage for LG is 2.00 V; the LR current-voltage graph has a linear high-current section and at 21.0 mA its forward voltage is 2.01 V.

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• AQA 7408 · November 2020 · Paper 1 · Q1 · 9 marks

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  Although some very good work was evident, there was much evidence of carelessness in the answers seen. Common errors included the incorrect value for the lepton number of a positive muon in 01.1, a failure to identify the uncharged nature of the particles in 01.2 and 01.3, and giving incomplete answers. In 01.4 in particular, many students only compared the rest masses of the particles and went no further.

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  This question concerns particle classification and interactions.

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• AQA 7408 · November 2020 · Paper 1 · Q2 · 12 marks

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  This question about the photoelectric effect proved to be very challenging to a significant number of students. In 02.1, many merely mentioned the threshold frequency without further explanation. Power of ten errors when reading the graph were common in 02.2. Parts 02.3, 02.4 and 02.5 were very poorly answered by the majority of students. A significant number attempted to answer the questions based on simple electricity andV IR = , for example. Answers indicated that many students were unfamiliar with the idea of stopping potential and there was a lot of confusion with work function.

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  A photoelectric-effect circuit measures photocurrent while the potential difference between a photoemissive surface and collecting anode is varied. With a constant-intensity monochromatic source, the maximum current is 30 microampere.

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• AQA 7408 · June 2019 · Paper 1 · Q1 · 7 marks

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  [1.2] Few students had any problem giving the correct answer to this question. In a small number of cases, the student gave too much information, so that it was unclear which part of it was their answer. In ‘state’ questions of this kind, students should be encouraged to write down just the answer expected, or at least to make the answer explicit.

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  Two iodine isotopes are I-125 and I-131.

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• AQA 7408 · June 2018 · Paper 1 · Q2 · 10 marks

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  [02.4] Most answers missed the point of the question. There were many responses that explained the excitation and de-excitation process, some in much detail, but did not explain clearly that the energy transfer to excite the electron in the atom has to occur with an exact amount of energy being supplied to the electron instantaneously. Many students quoted a ‘one to one interaction’, but this seemed to be a learned response and provided insufficient evidence of them understanding what this means.

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  Electron data (v/10^7 m s^-1,lambda/10^-11 m) are(1.5,4.9),(2.5,2.9),(3.5,2.1). A diffraction tube sends electrons through thin graphite to a fluorescent screen showing rings.

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• AQA 7408 · June 2017 · Paper 1 · Q1 · 10 marks

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  This question was generally well answered. In question 01.1, students had to complete the electron capture equation. While the majority were able to correctly identify the mass number and atomic number for argon, they were less successful at identifying the electron neutrino, with responses giving the particle as a neutron or gamma photon being quite common. Identifying the fundamental interaction involved as the weak interaction proved to be very accessible and over 80% of students were able to do this. They were less successful, however, in giving a reason. This was mainly because they did not refer to the interaction shown, giving answers which only mentioned leptons. They either needed to refer to the change of quark, or state that the interaction involved both hadrons and leptons. The calculation in question 01.3 was well answered and over two-thirds of students scored full marks. The common errors for those who did not were either failing to convert energy to joules, or a power of ten mistake. Question 01.4 was an example of students being required to make a judgement, and many good responses were seen. A significant proportion of students did, however, give generic answers indicating how they would distinguish between alpha, beta and gamma decay. This did not answer the question which required them to state what interaction was occurring to produce calcium–40 from the potassium isotope.

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  Potassium-40 is used to date rocks. It decays mainly to argon-40 by electron capture and can also decay to calcium-40 by a second process.

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