GCE Physics. PHYB5 Energy under the microscope Report on the Examination June 13. Version: 1.0

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1 GCE Physics PHYB5 Energy under the microscope Report on the Examination 2455 June 13 Version: 1.0

2 Further copies of this Report are available from aqa.org.uk Copyright 2013 AQA and its licensors. All rights reserved. AQA retains the copyright on all its publications. However, registered schools/colleges for AQA are permitted to copy material from this booklet for their own internal use, with the following important exception: AQA cannot give permission to schools/colleges to photocopy any material that is acknowledged to a third party even for internal use within the centre.

3 General Comments The paper seemed to be relatively accessible to candidates. Surprisingly, it was question 5 (about particle accelerators) that many of them found to be a little difficult. Overall there were few unattempted part questions and there did not seem be any timing difficulty for candidates. There were some pleasing examples of mathematical work. In some of the lengthier, multistage calculations there were some good examples of how to set work out clearly and effectively. As usual, candidates who managed this tended to be far more successful with their mathematical work. Some of the explanations tested the understanding of candidates. Some answers were very general when detail was required and, from time to time, there was some plain guessing going on. Answers to question 3 (c) were a little disappointing. This was the extended answer and full marks were rare as candidates tended not to answer the full scope of the question. Elsewhere, mistakes in interpreting questions were rare. Question 1 Part (a) (i) was answered correctly by most candidates. The most frequent errors occurred in the nucleon and proton numbers for the carbon. Where there were errors it was surprising to see that candidates did not tend to maintain consistent values of the numbers across the equation. In (a) (ii), most candidates mentioned that there tended to be a multiplicity of neutrons released in fission but many were unclear about the role of neutrons in producing fission. It was common to see answers suggesting that collisions with fissile nuclei caused fission. Candidates should have commented on the need for neutrons to be absorbed by the fissile nucleus. Part (b) (i) was quite well answered. The most common error was to confuse the absorption cross section with the actual size of the nucleus. A significant number of candidates also seemed to think that the area was to do with the distance of closest approach and therefore derived from the sum of the radii of the neutron and the nucleus. Many candidates knew that the barn was the unit of cross section but many did not. In part (b) (iii), a large number of candidates seemed to confuse the moderator and the control rods. However, the majority knew that the moderator slowed down the neutrons even if they were unclear about why that was necessary. Once again, imprecise use of vocabulary was a problem. Many candidates suggested that the slower neutrons were more likely to be absorbed without specifying that they were to be absorbed by the fissile nuclei. Candidates did not tend to understand the importance of the absorption cross section of the moderator nuclei. They had been expected to realise that a small absorption cross section was important to ensure neutron economy. In 1 (c) (iii), few candidates realised that the mass of the moderator nuclei influenced their capacity to slow the neutrons. Those that did realise this usually thought that heavier moderator atoms would be more effective than light atoms. There were some pleasing answers explaining the role of momentum exchange in the process. 3 of 6

4 Question 2 Most of the candidates made significant progress in part (a) and there were some very good explanations of thermionic emission. The most common omission was in not describing the role of the electric field between the anode and cathode in accelerating the electrons in the beam. Many candidates calculated the acceleration correctly and a significant number set out their work clearly and well. Some attempted to use the work done by the electric field between and others tried to use just the equations of motion. Parts (b) (ii) and (b) (iii) were well done by many candidates. In part (b) (iv), a significant number of candidates did not know how to proceed but the majority made some progress either by using ratios or equations of motion. For those that made significant headway, the most frequent mistake was to omit to add on the vertical distance that had already been travelled by the time the beam reached the end of the plates. Question 3 There were some pleasing complete, well-structured responses to part (a) (i). Some candidates thought that binding energy reduced during the reaction. The main error was to fail to mention the kinetic energy of the products of the reaction. Part (a) (ii) elicited the full range of responses including some well worked complete answers. Some managed to calculate the mass defect but could not convert this to amu and subtracted rather than added the mass defect in the final step. Most candidates had some idea of what constituted a plasma but many were a little hazy or unclear about how one should be produced. The calculation in (b) (ii) was generally well done. Some candidates lost marks by not stating a full equation with a subject at the start of the calculation. Candidates should be reminded that clarity and completeness is a requirement of show that type questions. A large minority of candidates made no attempt at the calculation in part (b) (iii). Some of those who attempted the part made a mistake in selecting the correct equation. However, there were a good number of successful answers. Many candidates just missed full marks because they had not noticed the different temperature that was indicated in this part. Only a very few realised that the energy available would twice the particle kinetic energy, as there were two ions involved. There were many competent answers to part 3 (c) but few that scored maximum marks. The whole range of the requested topics was not covered by the majority of candidates. In particular details of the shape of the vessel and the movement of the plasma were rarely given. Also, candidates did not tend to explain why it was necessary to use superconducting magnets, even when they had given a good explanation of the meaning of superconductivity. 4 of 6

5 Question 4 All of the subsections in part (a) were quite well answered with the exception of part (a) (v). Candidates should be advised to be specific in their answers. In this case, many candidates mentioned that the area represented work done without relating the work done to the exhaust and/or induction strokes. Many candidates found the work done in part (b) correctly but quite a few tried to use the product of pressure and volume change for arbitrary parts of the cycle. Some candidates set out their work when using the area method. It is notable that those who do so tend to get the whole answer correct more frequently and, even if they make a mistake, they tend to acquire more compensatory marks. Most candidates made a reasonable attempt to calculate the energy used to produce the heated steam. One common error was to omit the latent heat of vaporisation. Others were to add 273 to their temperature differences or to make powers of ten errors. Part (c) (ii) was done correctly by many but perhaps more made the common error of not using absolute temperatures. In Part (c) (iii), many candidates mentioned the idea that energy that would otherwise have been wasted was being used by steam. Fewer candidates thought of adding that the steam used the energy to do work on the piston. In the final part of the question there were many correct and complete answers. There are problems in this topic with careful and precise expression of ideas. Many candidates thought that the steam did work on the system, not realising that in this topic, the word system refers to the working fluid. Many candidates also thought that writing W was the equivalent of stating that W is negative. This is not the case. Question 5 The majority of candidates were too general in their answers to (a) (i) using statements such as to investigate sub-atomic particles. Often, when candidates did identify that the energy was used to create new particles, they thought that smaller particles could be found by using higher energies. There were many good answers to part (b) (i) with the major error being to forget to refer to the appropriate equations. Candidates found the explanation in part (b) (ii) more difficult. Many candidates confused cyclotrons with synchrotrons and others thought that the magnetic fields were for increasing the speed of the particles. Those who knew the topic gave good, succinct answers. The calculation in part (c) was often very well done. The most common error was to omit the relativistic mass part of the calculation. Other candidates are uncomfortable with ev. In (d) (i), most candidates could state at least one valid advantage. However, very general statements such as easier to build and less complex were not considered to be creditworthy. Candidates should be advised to attempt to be exact in their answers. For example can be run continuously was not thought to be the equivalent of produces a continuous beam The great majority of candidates could quote one or more valid uses for low energy cyclotrons. 5 of 6

6 Question 6 Part (a) (i) was generally well answered although some candidates did not attempt to explain the significance of the number 99. Similarly, most candidates made some positive response to part (a) (ii) but few made sufficient responses to gain full credit. Candidates should pay attention to the mark allocations provided. The majority of candidates produced complete, correct solutions to (b) (i). A sizeable minority made no attempt or had no clear idea how to proceed. Common errors among those who got partial solutions was a failure to assess the number of nuclei by failing to use Avagadro s number or the nucleon number. There were also some power of ten errors. There were also many confident and correct answers to part (b) (ii) but there was some evidence that a minority of candidates could not handle logarithms. In the final part of the question, there was evidence that fewer candidates were happy handling a question involving exponentials. Some candidates took a route that avoided finding the half thickness first and therefore penalised themselves. Many did not see the point of using more than one data set from the graph to determine an average value of half thickness. Others converted to metres and introduced a power of ten error. Mark Ranges and Award of Grades Grade boundaries and cumulative percentage grades are available on the Results Statistics page of the AQA Website. Converting Marks into UMS marks Convert raw marks into Uniform Mark Scale (UMS) marks by using the link below. UMS conversion calculator 6 of 6

A-LEVEL MATHEMATICS. MM04 Mechanics 4 Report on the Examination June 16. Version: 1.0

A-LEVEL MATHEMATICS. MM04 Mechanics 4 Report on the Examination June 16. Version: 1.0 A-LEVEL MATHEMATICS MM04 Mechanics 4 Report on the Examination 6360 June 16 Version: 1.0 Further copies of this Report are available from aqa.org.uk Copyright 2016 AQA and its licensors. All rights reserved.