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Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers PHYSICS Paper 9702/11…
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Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers PHYSICS Paper 9702/11 Multiple Choice Question Question Key Key Number Number 1 D 21 C 2 B 22 C 3 C 23 B 4 B 24 B 5 B 25 C 6 A 26 B 7 D 27 A 8 B 28 D 9 B 29 A 10 C 30 C 11 A 31 A 12 A 32 C 13 A 33 A 14 C 34 D 15 C 35 A 16 C 36 B 17 A 37 D 18 B 38 B 19 C 39 B 20 A 40 D General Comments This multiple choice paper is set on just the AS part of the syllabus and, with 40 questions to be answered within the time limit of an hour, accurate and quick working is essential. Candidates must know that they should not spend too long on any one question. Many questions need written working if candidates are to maintain accuracy. There is plenty of space on the paper and candidates should make use of it. One question, Question 21, was answered correctly by more than 80% of the candidates and four, Questions 29, 30, 33 and 36, were correctly answered by less than 20% of the candidates. 1 © 2011 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers Comments on Specific Questions Questions 1, 3, 12, 15, 17, 18, 19, 21, 22, 25, 38 and 40 were correctly answered by 60% or more of the candidates. There was a large gap covering Questions 26 to 37. This indicates that the waves and electricity sections of the syllabus are less well understood than the rest of the syllabus. Questions where there were many candidates making the same mistake were as follows. Question 6 43% of candidates did not allow a longer time for the ball to return to the slope after its inelastic collision with the wall. The inelastic collision causes a loss of speed. There were another 24% who chose option C, which shows a deceleration much larger than the acceleration on the friction- free slope. The acceleration due to gravity should be constant. Question 8 Candidates should remember that g is a constant. 41% thought A was correct and 32% thought D was correct. Question 10 Only 29% knew that C was the definition of force; 59% incorrectly answered A. Question 11 35% of candidates thought that D was the correct answer. Question 24 All four options were more or less equally chosen, suggesting that many candidates guessed. Only 27% chose the correct answer. Question 27 All four options were similarly popular here too. Candidates do need to know approximate values of wavelengths. That the (narrow) visible band of wavelengths is centred on green at 5.0 × 10–7 m is a useful figure to start with. Question 28 21% were correct here. Cover up one slit and the wave amplitude is halved, so the intensity is one-quarter. Question 29 Here only 16% gave correct answers. This does need care to see that both pipes will give a stationary wave. Question 30 This seemed straightforward with answer C but it had only 17% choosing it. A and B were both popular. The phase difference between the waves from P and Q is constant along the line RS, so there can be no interference pattern along RS. 2 © 2011 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers Question 32 This was another question with the four options more or less equally chosen. This suggests that many candidates guessed rather than using up time doing a proper analysis. 25% did get the correct answer. Question 36 41% gave D as the correct answer instead of B. Candidates would benefit from additional support in understanding the difference between p.d. and e.m.f. 3 © 2011 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers PHYSICS Paper 9702/12 Multiple Choice Question Question Key Key Number Number 1 C 21 C 2 D 22 A 3 D 23 B 4 D 24 D 5 B 25 B 6 C 26 B 7 B 27 B 8 D 28 A 9 D 29 D 10 B 30 A 11 A 31 A 12 D 32 C 13 D 33 D 14 B 34 A 15 B 35 A 16 B 36 C 17 A 37 B 18 D 38 A 19 A 39 C 20 A 40 C General Comments This multiple choice paper is set on just the AS part of the syllabus and, with 40 questions to be answered within the time limit of an hour, accurate and quick working is essential. Candidates must know that they should not spend too long on any one question. Many questions need written working if candidates are to maintain accuracy. There is plenty of space on the paper and candidates should make use of it. Only four questions were answered correctly by more than 80% of candidates and only two, Questions 15 and 31, had less than 25% of candidates obtaining the correct answer. 4 © 2011 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers Comments on Specific Questions Questions that produced more than 50% of correct responses were Questions 2, 3, 4, 5, 6, 7, 8, 11, 13, 14, 16, 17, 18, 19, 20, 22, 24, 27, 29, 30, 32, 33, 36, 37 and 40. Other questions where there was an unexpected outcome were as follows. Question 1 This was answered correctly by only 43% of candidates; 39% thought that the electronvolt measured electric potential. Candidates should be advised that the eV is a unit of energy. Question 9 Only 45% of candidates realised that, without knowing the mass of the ball, its acceleration cannot be determined. Question 10 50% of candidates incorrectly thought that the truck would speed up at Y. Candidates should consider conservation of the total momentum of the truck and sand, rather than considering the truck in isolation. Question 12 The subtraction of vectors always requires care to be taken. (It often produces surprising results, as with the acceleration of a body travelling in a circular path.) Question 15 Many candidates forgot to add on the original 4 J here. Questions 21 and 23 With both of these questions, interpreting the graphs proved difficult. Question 28 Many candidates did not realise that white light will produce a few fringes. Question 31 This question was the most difficult, with only 16% correct. The direction of field lines is the direction of the force on a positive charge. So the answer is A, the charge being negative. C had 51% responses. 5 © 2011 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers PHYSICS Paper 9702/13 Multiple Choice Question Question Key Key Number Number 1 C 21 B 2 D 22 B 3 B 23 C 4 B 24 C 5 B 25 B 6 D 26 C 7 A 27 D 8 B 28 A 9 B 29 C 10 A 30 A 11 C 31 C 12 A 32 A 13 C 33 D 14 A 34 A 15 C 35 A 16 A 36 D 17 C 37 B 18 C 38 B 19 A 39 D 20 B 40 B General Comments This multiple choice paper is set on just the AS part of the syllabus and, with 40 questions to be answered within the time limit of an hour, accurate and quick working is essential. Candidates must know that they should not spend too long on any one question. Many questions need written working if candidates are to maintain accuracy. There is plenty of space on the paper and candidates should make use of it. Six questions were answered correctly by more than 80% of candidates. At the other end of the scale, only Questions 29, 35 and 38 had less than 25% of candidates obtaining the correct answer. 6 © 2011 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers Comments on Specific Questions Questions that produced more than 50% of correct responses were Questions 1, 2, 4, 5, 6, 10, 11, 12, 13, 14, 15, 16, 18, 19, 20, 23, 24, 26, 28, 32, 33, 34, 36, 37, 39 and 40. Other questions where there was an unexpected outcome were as follows. Question 3 Many candidates ignored the fact that the diameter of the wire is squared, giving an uncertainty of about 7% for this term. Question 7 41% of candidates did not allow a longer time for the ball to return to the slope after its inelastic collision with the wall. The inelastic collision causes a loss of speed. There were another 19% who chose option C, which shows a deceleration much larger than the acceleration on the friction- free slope. The acceleration due to gravity should be constant. Question 8 The stem of the question states that the body does reach terminal velocity, so the height from which it falls does not affect its terminal velocity. All the other statements do, but these each gained about 20% of choices made by candidates. Question 9 Candidates need to remember that g is a constant. 24% thought A was correct and 27% thought D was correct. Question 21 E is a constant for a particular type of steel, but 39% of candidates thought 2E was the correct answer, the same percentage as had the correct answer B. Question 22 The first three options were more or less equally chosen, suggesting that many candidates guessed. Only 30% chose the correct answer. Question 25 This was another question where the first three answers were almost equally chosen. Once the Young modulus equation is rearranged Δ l ∝ l / l 2 makes answer B clear. Question 27 The correct answer here was given by 36%. Cover up one slit and the wave amplitude is halved, so the intensity is one-quarter. Question 29 Only 23% realised that the interference pattern is only along XY (although there can be one along PQ, but that was not an option). A and B were both more popular choices. The phase difference between the waves from P and Q is constant along the line RS, so there can be no interference pattern along RS. 7 © 2011 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers Question 30 Here there were only 33% correct answers. This does need care to see that both pipes will give a stationary wave. Question 35 This question was the most difficult on the whole paper, with 14% of responses correct. Careful analysis is needed to sort out the correct response and this must be done by careful working—for which there is plenty of space. Question 38 36% gave D as the answer instead of B. Candidates would benefit from additional support in understanding the difference between p.d. and e.m.f. 8 © 2011 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers PHYSICS Paper 9702/21 AS Structured Questions Key Messages ã Many candidates would benefit from taking a moment to consider the numerical answers that they have obtained, especially as regards powers of ten. A quick check on whether an answer is ‘reasonable’ would allow candidates to detect errors in their working. ã Candidates should be encouraged not to ‘round off’ answers at intermediate stages of a calculation, as this can lead to inaccurate and inappropriate final answers. ã Candidates should be advised to use the data given on page 2 of the question paper. In particular, the –2 use of the approximation g = 10 m s should be discouraged. ã The application of knowledge of basic concepts to unfamiliar situations is often found to be difficult. Candidates who have difficulty would improve their performance if they spent time discussing and practising the application of basic concepts to new situations. ã Most candidates could improve their performance by learning the precise details of definitions and laws required by the syllabus. The wording of answers should relate to the question asked and a certain amount of precision is required at this level. A vague statement of the terms involved is generally not sufficient. General Comments There were few candidates who did not complete their answers to questions. There was no evidence amongst adequately prepared candidates of a shortage of time. Candidates appeared to find some parts of all questions difficult. Responses did vary considerably with Centres. Candidates should be encouraged to read carefully through any question before making any attempt with an answer. Generally the mark allocation indicates the required length and complexity of any answer. Candidates should be made aware of the need to give specific detail included in the question when asked to give explanations. Comments on Specific Questions Question 1 (a) Generally definitions were satisfactory. Candidates should be advised that where equations are given as definitions then all symbols should be defined. (b) The great majority of statements did not answer the question that was asked. Candidates needed to read the question carefully and use the variation in the spacing of the molecules to explain the difference in the densities of solids, liquids and gases. (c) (i) A significant number of candidates obtained the correct answer. The weaker candidates had difficulty with the units and powers of ten. 9 © 2011 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers (ii) Weaker candidates were able to gain partial credit for the equation for pressure. The more able candidates realised that the force required the weight of the slab and that maximum pressure is obtained with the smallest area. Question 2 (a) The majority of candidates did not give enough detail in their definition. Candidates should be reminded that a precise definition is needed in order to obtain full credit. (b) (i) This was generally well answered by the well prepared candidates. (ii) A significant number of candidates recognised that the rod was not in equilibrium. The explanations given did not always describe the reasons in detail. (c) (i) The majority of candidates did not take moments about one point. Candidates should be encouraged to practise questions where there are two unknown forces to be determined. (ii) A number of candidates were able to gain credit by realising that the resultant force in the vertical direction was zero. Question 3 (a) Most answers were correct. Candidates should be encouraged to give some working rather than merely writing down an answer. (b) (i) A significant number of candidates used an appropriate equation of motion and calculated the height correctly. Candidates should be encouraged to practice questions where the motions in a horizontal direction and vertical direction are treated separately. (ii) The majority of answers were correct. (iii) Many candidates did not realise that the time to return to the ground was the same as in (ii), the time for the upward journey. (c) (i) The majority of candidates were unable to determine the initial momentum of the ball although the correct value for the horizontal component had been determined in (a)(i). There were very few correct answers for the change in momentum. (ii) This was generally well answered. Some candidates showed some confusion with conservation of energy, conservation of kinetic energy or conservation of momentum Question 4 (a) The majority of candidates were unable to explain the difference between the two types of potential energy. It was expected that candidates should know that the key elements for the different potential energies were mass and charge. (b) The derivations often lacked any explanation. Candidates should be encouraged to give solutions with an explanation of the symbols used and a statement between each step. (c) (i) There were a number of good solutions. A significant number of candidates found difficulty with the calculation involving a percentage. (ii) Very few candidates obtained the correct answer. Again the efficiency calculation caused difficulty for the majority of candidates. Candidates would benefit from greater emphasis being placed on the application of basic principles to everyday situations. 10 © 2011 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers Question 5 (a) Many candidates were not able to give an acceptable definition. (b) Candidates generally gained at least partial credit for giving the defining equation for resistivity or its units. (c) (i) A significant number of candidates obtained the correct answer. (ii) The majority of candidates were unable to interpret the series circuit and obtain the correct distribution of the potential difference across the two resistances. (iii) Well prepared candidates calculated the correct answer. (d) (i) There were a number of correct answers. Application of a formula caused problems for some candidates. (ii) Very few candidates were able to give the correct answer. Candidates did not appear to realise the effect on the circuit of adding a resistance with a very large value. Question 6 (a) Well prepared candidates gave the correct definition. A significant number of candidates were unable to give the required definition. (b) (i) There were very few answers given with the required precision. A common error was to include a vague reference to a limit rather than the point beyond which the object does not return to its original length. Many candidates also omitted the condition of ‘when the force is removed’. A significant minority also confused the elastic limit with the limit of proportionality. (ii) A significant number of candidates were able to determine the correct value. There were powers of ten errors and misreading of the scales by the weaker candidates. (iii) A number of candidates were able to obtain the correct value. A significant number of candidates used an inappropriate equation for the work done extending a spring. (c) This part tested the understanding of the term ‘spring constant’. Very few candidates were able to demonstrate a good understanding and hence correct answers were seldom seen. Candidates would benefit from further experience of solving problems involving spring constants. Question 7 (a) The required explanation of an isotope was not well known by a large number of candidates. Candidates must refer to nuclei in their explanation of isotopes. (b) (i) Very few candidates were able to give the required quantity conserved in a nuclear reaction. (ii) Well prepared candidates completed the analysis and gained full credit. It was clear that many candidates had not had sufficient practice with these types of reactions. (c) A common error was to not to include the neutron absorbed by the uranium nucleus. 11 © 2011 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics November 2011 Principal Examiner Report for Teachers PHYSICS Paper 9702/22 AS Structured Questions Key Messages ã Many candidates would benefit from taking a moment to consider the numerical answers that they have obtained, especially as regards powers of ten. A quick check on whether an answer is ‘reasonable’ would allow candidates to detect errors in their working. ã Candidates should be encouraged not to ‘round off’ answers at intermediate stages of a calculation, as this can lead to inaccurate and inappropriate final answers. ã Candidates should be advised to use the data given on page 2 of the question paper. In particular, the –2 use of the approximation g = 10 m s should be discouraged. ã The application of knowledge of basic concepts to unfamiliar situations is often found to be difficult. Candidates who have difficulty would improve their performance if they spent time discussing and practising the application of basic concepts to new situations. ã Most candidates could improve their performance by learning the precise details of definitions and laws required by the syllabus. The wording of answers should relate to the question asked and a certain amount of precision is required at this level. A vague statement of the terms involved is generally not sufficient. General Comments There were few candidates who did not complete their answers to questions. There was no evidence amongst adequately prepared candidates of a shortage of time. Candidates appeared to find Questions 3, 5 and 7 to be the most difficult. Responses did vary considerably between Centres. Candidates should be encoura
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