A-LEVEL PHYSICS A. PHA6T Investigative and Practical Skills in A2 Physics (ISA) Report on the Examination June Version: 0.

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1 A-LEVEL PHYSICS A PHA6T Investigative and Practical Skills in A2 Physics (ISA) Report on the Examination 2450 June 2014 Version: 0.1

2 Further copies of this Report are available from aqa.org.uk Copyright 2014 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 Reports from moderators suggested that ISA P (Conical Pendulum) was very slightly more popular than ISA Q (Thermistor). Feedback from centres suggested both experiments worked well, enabling candidates to take the data required. A small number of centres had initial problems selecting suitable thermistors, but overall apparatus requirements posed no significant problems. Most Centres dealt with administrative issues efficiently, ensuring that scripts, Centre Marksheets, Centre declaration Forms and Candidate record forms were delivered to moderators by the prescribed deadline. There were, however, a significant minority of centres where scripts arrived late or with missing documentation. Unfortunately arithmetic and transcription errors were again discovered on a small proportion of the scripts sampled. This continues to be a concern. It is the centre s responsibility to ensure correct addition of PSA marks to the marks for each section of the ISA test. Although some errors are discovered and corrected by moderators only a proportion of scripts are checked and remarked in the moderation process, with the possibility of other errors left undiscovered. Printing of ISA papers was inadequate from a few centres where graph grids did not show the fine grid lines required for plotting, checking points, and reading data for gradient calculations. It is essential that any copying process produces graph pages sufficiently detailed to allow candidates access to the marking points allocated for the graph in question 2. The standard of marking was very good in most cases, with markers carefully following the mark scheme. Reports from moderators suggest there was a definite increase this year in the number of centres where marking was outside the tolerance. There were also a small but significant number of centres with scripts where marking was 10 or more marks different to the moderated mark. Where centres are out of tolerance an adjustment to centre marks will be made. The most common marking errors were almost identical to previous years, and included awarding credit for: Unsuitable graph scales Incorrectly plotted graph points Poor quality best fit curves. Although allowance is made for the difficulty in drawing a freehand smooth curve, many of the lines credited were too thick, overdrawn several times, disconnected in places or lines which joined point to point Missing units in questions where the mark scheme specifically stated that the correct unit was required. Incorrect significant figures where this had been specified as part of the marking point Weak explanations, not fulfilling the requirements specified in mark scheme Awarding the mark for one point mentioned in the mark scheme where two or more points are required for the one mark. 3 of 8

4 Some teachers seem unaware of the advice on marking issues available from their Assessment Advisors. AQA informs centres every year of the contact details of Assessment Advisors in each subject. In stage 1 of the ISA candidates should be provided with separate sets of apparatus so that they can perform the experiment on their own, talking their own unique sets of data. This is made clear in the instructions to centres. Sharing of apparatus by two or more candidates is not allowed. In situations where centres cannot provide enough sets of apparatus so that all their candidates can perform the experiment at the same time, arrangements should be made for additional practical sessions. There were a small but significant number of cases where students had clearly worked together, in pairs or in one case four candidates with shared results. Candidates cannot access many of the marking points in stage 1 if the data presented is not their own and marks will usually be deducted. ISA P Conical Pendulum Stage 1 This was a demanding experiment, requiring skilful timing techniques. Almost all candidates were able to take a satisfactory set of results, which produced an obvious curved line on the graph. Candidates of all abilities were able to score well on this section with most achieving 6 or 7 marks. The most common mistakes were: Failure to take repeat readings of the circular path Unrealistic judgement of uncertainty in measurement of length of the string. Poor graph scales which could have been doubled Incorrectly plotted points Poor quality lines of best fit (curves). ISA Test Paper Question 1 (i) (ii) (iii) (iv) Correctly answered by a large proportion of candidates. Less able candidates were confused by the requirement to convert uncertainties in d and l into percentage uncertainties before combining to give the percentage uncertainty in cosθ. Some candidates incorrectly doubled the percentage uncertainty in l because 2l appeared in the formula for cosθ. A few candidates lost credit for quoting too many significant figures. A straightforward calculation answered well by a large majority of candidates. A few candidates lost credit by missing the unit. This question proved much more demanding and discriminated well. Most candidates realised that the uncertainty in d did not contribute to the uncertainty in F. The contribution of T and l were more difficult to explain, with many candidates failing to refer to the combination of percentage uncertainties rather than uncertainty. More able candidates realised that since T was squared, the percentage uncertainty would be doubled in its contribution to the uncertainty in F. 4 of 8

5 A difficult question for most candidates with only a small proportion scoring both marks. Since the graph was a curve the first point to make was that the increase in T with l was non-linear. The second marking point was much more difficult, requiring a description of how the gradient of the curve changed in terms of the rate of increase decreasing. This proved to be difficult for most candidates, with only the most able realising that a vertical component of the tension is needed to support the weight of the mass. Question 2 (d) As usual the table was correctly completed by almost all candidates. A small proportion of candidates lost marks on point plotting and the line of best fit. Most candidates scored 2 marks on this question. The most common error was misreading data from the graph or using data points not actually on the line. This was a straightforward calculation for most candidates, who scored the full 2 marks. A few candidates lost the marks by providing a calculation without using their gradient value and a very small proportion lost credit by missing the unit. (e)(i) Similar to 2 in that a large proportion of candidates correctly computed the value of g. Less able candidates got mixed up with the algebraic rearrangement and some did not follow the instruction to use the answer in 2. A small proportion of candidates lost one mark for a missing or incorrect unit. (ii) (iii) An easier question answered well by most candidates, requiring reference to the closeness of points around the line of best fit. This question was more difficult and discriminated well. Again a lack of understanding of the difference between uncertainty and percentage uncertainty caused problems. A smaller radius gives a larger time period so the percentage uncertainty in T is smaller. (The uncertainty in T is not smaller a common error by many candidates). The second mark was generally more accessible, leading to a conclusion that the uncertainty in g would be smaller. To access this mark the conclusion must be consistent with the response to the first marking point. 5 of 8

6 Question 3 This question was answered well by middle and higher grade candidates. The most common response was to quote the algebraic equations to show that θ does not depend on m. A brief outline was required in this question. Any simple method of measuring the time period of rotation and the diameter of the circle was acceptable. This was a much more demanding question with five possible marking points for the three marks. Only the most able students scored the full three marks. Question 4 Many lengthy answers were confused, demonstrating they had not understood the idea of mathematically calculating the tension in the chains when the chair was fully loaded and rotating at maximum angular speed, and then performing a stationary test to exceed this tension. Many candidates were able to score one or perhaps two marks without a full understanding of the process. This proved to be a demanding question and discriminated well. Only the most able candidates scored the full four marks, with many less able candidates unable to access any of the marking points. It was clear from many responses that candidates didn t fully understand the process involved, and consequently there were many lengthy descriptions of unworkable experiments. Many candidates missed the statement that the turntable rotated at a known constant speed, and incorrectly based their experiment on increasing the turntable speed until the disc slipped. The most accessible marking point was a statement of the graph to plot, (marking point F). 6 of 8

7 ISA Q Thermistor Stage 1 The experiment worked well, and in the majority of cases produced an obvious smooth curve. Candidates of all abilities were able to score well on this section with most achieving 6 or 7 marks. The most common mistakes were: Poor graph scales which could have been doubled Incorrectly plotted points Poor quality lines of best fit (curves) ISA Test Paper Question 1 (i) (d) (e) A straightforward percentage uncertainty calculation answered well by most candidates. Most candidates were able to calculate the percentage uncertainty of the thermistor resistance at room temperature by adding the percentage uncertainties in current and pd. Only the more able candidates were able to access the second mark by converting the percentage uncertainty back to an (absolute) uncertainty in the resistance value. A small proportion of candidates lost a mark by either quoting too many significant figures or missing the unit in the final uncertainty value. Most candidates scored one mark but only the most able managed to get the full two marks. The most common correct response was reference to stirring the water. This question discriminated well, with only the more able candidates accessing the second mark. Most candidates realised that a larger current would produce a significant heating effect, but very few went to explain that this would result in the temperature of the thermistor being different to the measured temperature of the water. A difficult question for many candidates, although more able students were able to access both marks. The most common correct response was to plot a graph of lnr against θ, expecting a straight line with a negative gradient. Question 2 (d)(i) As usual the table was correctly completed by almost all candidates. A small proportion of candidates lost marks on point plotting and the line of best fit. A significant proportion of candidates lost a mark on this question. The most common errors was misreading data from the graph, using data points not actually on the line and failing to include the 10-3 factor on the x-axis. Answered correctly by most candidates, although incorrect or missing units resulted in one mark lost on some scripts. 7 of 8

8 (ii) (iii) This question proved to be more discriminating with the requirement to use a value for lnr and 1/T taken from the line of best fit, and then substitute into the formula. Many students incorrectly read the y-intercept for lna, failing to realise that both graph axes do not start at the origin. A few marks were lost by omitting the unit of A. Answered reasonably well all but the least able candidates. Question 3 This question did not discriminate as well as expected, with a relatively large proportion of candidates scoring 3 or 4 marks. The most common error was a missing or incorrect unit on the final answer. The second part of the question proved to be more demanding. Only the more able students appreciated the significance of the data from 3. Question 4 This question discriminated quite well, with only more able candidates scoring 2 or 3 marks. Ohm-meters were incorrectly used by some students, by connecting to a circuit with a separate power supply. Many students failed to explain the use of the calibration graph to determine temperature. The second part of this question proved to be much more accessible with a large proportion of candidates scoring the full two marks. The idea of plotting a p-t graph and extrapolating it back to get the intercept on the T axis was well known. 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 8 of 8

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