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Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers PHYSICS Paper 9702/11 Multiple…
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Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers PHYSICS Paper 9702/11 Multiple Choice Question Question Key Key Number Number 1 A 21 D 2 D 22 B 3 C 23 C 4 D 24 B 5 C 25 B 6 C 26 C 7 D 27 B 8 B 28 B 9 D 29 C 10 D 30 C 11 B 31 D 12 A 32 C 13 C 33 C 14 D 34 A 15 D 35 C 16 B 36 B 17 C 37 A 18 B 38 C 19 D 39 A 20 D 40 B General comments There were some straightforward questions that were answered correctly by most candidates. Other questions were more demanding, with a significant proportion of candidates not giving the correct response. This spread of difficulty of the questions was intentional so that the paper, as a whole, differentiated as well as possible between candidates of different abilities. Candidates should be advised to concentrate on the AS part of the syllabus when preparing for this paper. Furthermore, they should be aware that, on average, each question should be completed in 90 seconds. They should ensure that the available time is spread out over the whole paper. Space is provided on the question paper for rough working. Candidates should not rely solely on mental agility when answering questions. Having decided on one of the possible answers, candidates should be encouraged to ask themselves whether the answer is reasonable so that they avoid trivial errors such as powers-of-ten. 1 © 2012 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers Comments on specific questions Questions 7, 20, 26, 28 and 33 were answered correctly by the great majority of candidates. Question 4 This question was answered correctly by the more able candidates. Lower-scoring candidates tended to opt for either A or C. Question 5 The very popular incorrect response was D. Candidates should realise that any uncertainty should be expressed to one significant figure. Question 8 Although more able candidates did give the correct response, a large proportion of lower-scoring candidates assumed that the feather would fall with constant speed, despite being in a vacuum. Question 10 Nearly all candidates opted for either B or D. Option D was favoured by higher-scoring candidates. The syllabus specifies that force is defined as the rate of change of momentum. Question 12 This proved to be a difficult question with answers almost equally spread amongst the options. Clearly, candidates were not familiar with this type of question. Question 13 This was answered correctly by higher-scoring candidates, but options A and D were popular alternatives. Question 15 This question proved to be difficult for lower-scoring candidates with the three incorrect responses being chosen by approximately equal numbers of candidates. Question 18 The most popular answer was A, thus suggesting confusion between energy and power. Question 23 This question indicated a lack of understanding of the Young modulus. By far the most popular answer was option D with the correct response, C, being the least popular answer. The spring constant depends on the Young modulus, cross-sectional area and original length of a wire. Question 24 This item discriminated well, with higher-scoring candidates answering correctly. Other candidates were equally divided amongst the incorrect options. Question 31 Although this question was answered correctly by higher-scoring candidates, many others gave C as their choice. Question 34 The use of ratios would appear to be a problem for many lower-scoring candidates. 2 © 2012 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers Question 35 This item proved to be difficult but the more able candidates were successful. Option D was as popular an answer as the correct response. Question 36 The most common answer was D. The correct response, B, was given by the higher-scoring candidates but otherwise, there appeared to be much guesswork. Question 37 Potential divider questions do seem to cause difficulties for lower-scoring candidates. Popular incorrect responses were B and C. 3 © 2012 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers PHYSICS Paper 9702/12 Multiple Choice Question Question Key Key Number Number 1 C 21 C 2 D 22 C 3 D 23 C 4 B 24 B 5 B 25 C 6 A 26 D 7 A 27 C 8 D 28 D 9 A 29 C 10 A 30 B 11 B 31 C 12 D 32 C 13 A 33 D 14 B 34 B 15 D 35 D 16 D 36 D 17 B 37 D 18 D 38 C 19 B 39 B 20 D 40 B General comments There were some straightforward questions that were answered correctly by most candidates. Other questions were more demanding, with a significant proportion of candidates not giving the correct response. This spread of difficulty of the questions was intentional so that the paper, as a whole, differentiated as well as possible between candidates of different abilities. Candidates should be advised to concentrate on the AS part of the syllabus when preparing for this paper. Furthermore, they should be aware that, on average, each question should be completed in 90 seconds. They should ensure that the available time is spread out over the whole paper. Space is provided on the question paper for rough working. Candidates should not rely solely on mental agility when answering questions. Having decided on one of the possible answers, candidates should be encouraged to ask themselves whether the answer is reasonable so that they avoid trivial errors such as powers-of-ten. 4 © 2012 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers Comments on specific questions Questions 3, 11, 19, 27, 39 and 40 were answered correctly by the great majority of candidates. Question 4 This question was answered correctly by the more able candidates. Lower-scoring candidates tended to opt for option A. Question 5 The very popular incorrect response was D. Many candidates are confused as to the difference between accuracy and precision. Question 8 Although more able candidates did give the correct response, a large proportion of lower-scoring candidates 2 2 2 opted for C. Candidates frequently equate, quite incorrectly, (y – x) to (y – x ). Question 9 The correct response, A, was favoured by higher-scoring candidates. A popular misconception that the brick would fall with constant speed was indicated by the choice of B. Question 12 Answers were almost equally divided between option A and the correct answer D. The relative speed of approach should be equal to the relative speed of separation in an elastic collision. The interpretation of the directions appeared to cause problems. Question 13 This was answered correctly by higher-scoring candidates, but option B was very popular with lower-scoring candidates. This type of question appeared to be unfamiliar to many. Question 14 This question proved to be difficult with all the options being almost equally popular, indicating much guess- work. Question 15 A significant number of candidates appeared not to read the question carefully. They gave the torque produced by the cube and not the torque to maintain equilibrium. Question 26 As is often the case in such questions, many weaker candidates did not allow for the reflection of the wave thus giving the answer as option C. Question 30 The most common answer was option D but closely followed by the correct response, option B. There appeared to be confusion as to the relationship between wavelength and internodal distance. Question 33 A minority of candidates gave the correct response. The most common answer was option C with a significant number of more able candidates opting for B. Clearly, this topic is not well understood. 5 © 2012 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers Question 37 The only option where the lamps are lit dimly is the correct answer D. Many lower-scoring candidates opted for C where the lamps, although connected in series, are said to be lit normally. 6 © 2012 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers PHYSICS Paper 9702/13 Multiple Choice Question Question Key Key Number Number 1 C 21 B 2 A 22 C 3 D 23 B 4 C 24 D 5 D 25 D 6 D 26 B 7 C 27 C 8 D 28 C 9 B 29 B 10 A 30 C 11 D 31 D 12 B 32 A 13 D 33 C 14 C 34 C 15 D 35 B 16 C 36 C 17 B 37 C 18 D 38 A 19 B 39 B 20 B 40 A General comments There were some straightforward questions that were answered correctly by most candidates. Other questions were more demanding, with a significant proportion of candidates not giving the correct response. This spread of difficulty of the questions was intentional so that the paper, as a whole, differentiated as well as possible between candidates of different abilities. Candidates should be advised to concentrate on the AS part of the syllabus when preparing for this paper. Furthermore, they should be aware that, on average, each question should be completed in 90 seconds. They should ensure that the available time is spread out over the whole paper. Space is provided on the question paper for rough working. Candidates should not rely solely on mental agility when answering questions. Having decided on one of the possible answers, candidates should be encouraged to ask themselves whether the answer is reasonable so that they avoid trivial errors such as powers-of-ten. 7 © 2012 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers Comments on specific questions Questions 1, 6, 17, 25, 26, 27, 29 and 34 were answered correctly by the great majority of candidates. Question 4 The very popular incorrect response was D. Candidates should realise that any uncertainty should be expressed to one significant figure. Question 5 This question was answered correctly by the more able candidates. Lower-scoring candidates tended to opt for A. Question 9 Although more able candidates did give the correct response, a large proportion of lower-scoring candidates seemed undecided between the three incorrect responses. Question 10 This proved to be a difficult question with the majority of candidates opting for the incorrect response C. Clearly, candidates were not familiar with this type of question. Question 12 The higher-scoring candidates chose the correct response. The majority of lower-scoring candidates opted for D. Question 13 This question proved to be difficult for lower-scoring candidates with the three incorrect responses being chosen by approximately equal numbers of candidates. Question 14 This was answered correctly by higher-scoring candidates, but option D was a popular alternative. Question 19 The most popular answer was the correct response B, but nearly as many chose option A, thus indicating confusion between energy and power. Question 21 This item discriminated well, with higher-scoring candidates answering correctly. Other candidates were divided amongst the incorrect options with D being the most popular incorrect response. Question 22 This question indicated a lack of understanding of the Young modulus. By far the most popular answer was D. The spring constant depends on the Young modulus, cross-sectional area and original length of a wire. Question 28 Although the correct option, C, was favoured by higher-scoring candidates, many others elected for D, thus assuming the angle for the first order to be 70°. Question 31 Although this question was answered correctly by higher-scoring candidates, many others gave C as their choice. 8 © 2012 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers Question 35 The correct response, B, was given by the higher-scoring candidates but otherwise, there appeared to be much guesswork. Question 36 This item proved to be difficult but the more able candidates were successful. With lower-scoring candidates, there appeared to be a large element of guesswork. 9 © 2012 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers PHYSICS Paper 9702/21 AS Structured Questions Key messages ã Candidates should be encouraged to show all their working in numerical questions. The full equation should be shown with the substitution of the data before any calculations are made. Candidates who show clear presentation of their working tend to receive more credit and make fewer mistakes. ã There was evidence of incorrect rounding in some of the answers to numerical questions. Candidates should be encouraged to read values carefully from their calculators before giving answers to two or three significant figures. ã Candidates were asked to use their knowledge and understanding to explain particular phenomena, often in unfamiliar situations. The candidates’ descriptions were often lacked the required detail. Candidates should be encouraged to practise writing several sentences of continuous prose to give explanations of different phenomena in physics. Many examples of such exercises are to be found in past examination papers. 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. General comments Fundamental to a good performance in any examination is a sound knowledge of facts. However, some candidates appeared to be somewhat lacking in their knowledge and understanding of various aspects of the syllabus. Accurate recall of expressions is required but this was not evident in the work of weaker candidates. Where calculations are required, work should be set out clearly. Candidates need to be reminded that credit is awarded not only for answers, but also for the approach to problems. Some candidates did not give even a basic explanation of the method being used, but simply substituted numbers into unexplained formulae with unfamiliar symbols. If the resulting answer was incorrect, no credit could be awarded. Comments on specific questions Question 1 The majority of candidates found this question a straightforward start to the examination. (a) (i) This was answered correctly by almost all candidates. (ii) The majority of answers were expressed clearly. Credit was lost where candidates changed the power of units by crossing out or altering what they had written, making their final answer illegible. (b) Candidates should be advised to give the base units of each quantity in the form of an equation without any change of power. Only then should simplification take place, but on a different line of 4 working. The usual errors were associated with either missing out the factor of r or failing to give the power of four. 10 © 2012 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers Question 2 (a) (i) The majority of candidates answered this correctly. Very few candidates attempted the calculation using the assumption that g = 10 m s–2, which would not have provided the value given in the question. (ii) Again, the great majority of answers were correct. Almost all included the initial velocity of the ball. (b) (i) Only a minority of answers included an initial statement making reference to rate of change of momentum, and references to change of any quantity were rarely seen. Consequently, the majority included only the rebound velocity. Candidates who did appreciate that there should be a change, frequently found the difference between the magnitudes of the velocities, rather than the sum. Answers stating that the force would be downwards were in the minority. (ii) This was generally answered well, with only a minority using an incorrect value of speed when calculating the kinetic energy. (c) As the speeds before and after impact were given, candidates should have been able to deduce that the impact would be inelastic. A significant number thought that the collision would be elastic because the ball reached the same height as given in (a)(ii). Question 3 (a) Most candidates gave a general statement regarding forces in equilibrium. Very few then went on to refer to the forces acting on the mass. Candidates should be able to distinguish between tension in the spring and the force on the mass due to the spring. (b) There were a few candidates who gave correct answers for all three parts. However, many answers indicated a lack of understanding when trying to interpret the graph. A common error was to give the time for maximum speed as 0.40 s. (c) (i) There were many appropriate statements of Hooke’s law, although few correctly related the law to the graph in Fig. 3.4. A common misunderstanding was to state that mass is proportional to length, thus satisfying the law. (ii) In most cases, the gradient of the graph was used with few attempting a ‘one point’ solution. A significant number of candidates took the value of g to be 10 m s–2 and then made no comment as to why they had not obtained the value given for the force constant. Candidates should be advised always to use the data provided in the question paper. (iii) The majority of candidates gave a correct expression for stored energy (½kx2 or ½Fx), but many then assumed that x was the length of the spring rather than its extension. Question 4 This was generally answered well. (a) (i) Most answers were correct. A significant number of candidates, calculated the current and then used the expression V = IR, rather than calculating the resistance directly using the expression P = V2 / R. (ii) Again, the majority of answers were correct with very few errors being made when re-arranging the expression for resistivity. (b) (i) Almost all candidates calculated this correctly. Candidates should always consider the number of significant figures when giving their answers. (ii) Most answers did include a statement to the effect that the resistance must be reduced, but only the more able candidates gave a quantitative explanation. 11 © 2012 Cambridge International Advanced Subsidiary Level and Advanced Level 9702 Physics June 2012 Principal Examiner Report for Teachers Question 5 Many candidates found this question to be very demanding, and appeared not to have studied potential differences along a uniform wire. (a) (i) Frequently, the definition was given without reference to the sums of the e.m.f. or the potential differences. (ii) Many gave incorrect responses to this. Common answers were current, charge, p.d. and e.m.f. (b) (i) There were relatively few correct answers. In the majority of cases, the total resistance of the circuit CXYDC was not considered. (ii) An ‘error-carried-forward’ from (i) was accepted here, but this did not result in many candidates being given credit. Most answers involved the total resistance of the wire XY, rather than the resistance of the length XJ. (iii) Very few candidates appreciated that the e.m.f. would be equal to the answer given in (ii). In many scripts, this part of the question was not attempted. (iv) The most common answer was based on negligible internal resistance. Very few understood that the current in the internal resistor would be zero and consequently there would be no ‘lost volts’. Question 6 (a) (i) There were many references to ‘constant frequency’ and ‘constant wavelength’. Of the minority who did specify ‘constant phase difference’, few made any comment as to what would have this constant relationship. (ii) A small minority of candidates referred to the condition based on path difference or on phase difference. However, the majority described this in very elementary terms based on ‘crests’ and ‘troughs’. (iii) Again, this was very poorly answered using elementary terms. (iv) The majority
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