A-LEVEL PHYSICS B. PHYB4 Physics Inside and Out Report on the Examination June Version: 1.0

Transcription

1 A-LEVEL PHYSICS B PHYB4 Physics Inside and Out Report on the Examination 2455 June 2015 Version: 1.0

2 Further copies of this Report are available from aqa.org.uk Copyright 2015 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 Question 1 Weight was drawn correctly by most candidates, but friction was usually drawn away from the wall and some drew force pointing to the right, presumably to balance the forces. (a)(ii) Some candidates believed that reaction force and centripetal force were not connected, and the relation between friction and reaction was not appreciated. (i) Easy question. Some used diameter instead of radius. (ii) Many calculations erroneously used T = II Although N m for the unit was the majority answer, some gave the answer in kg, m and s, which if correct was credited, but answers which included rad were marked wrong, since rad is dimensionless. (iii) A mark was thrown away by many candidates, who did not realise that the appropriate number of significant figures was 2. (c)(i) Most plumped for C. (c)(ii) Very few mentioned the key fact that at C the speed is greater. Question 2 Well done. (a)(ii) Candidates scored 2 or zero. The latter invariably used centripetal force = gravitational force. (a)(iii) Many promising calculation were ruined by failure to cube the radius when finding the volume. Most candidates did not realise that escape velocity was not needed because the rocket was not escaping! Question 3 Mostly well done. (a)(ii) The three acceptable reasons were connected to the three terms in the formula: η, r and v. The commonest correct answer was that the vehicle would not be spherical and so r was meaningless. Good answers highlighted the effect of higher velocity in the air has no viscosity. Most candidates mentioned the lack of reaction force but some answers were spoilt by claiming that there was no resultant force or even no gravity. 3 of 5

4 (c)(i) Each step needed to be clearly shown, starting with the statement that gravitational force = centripetal force. There were several cases of the use of 900 km for the radius. (c)(ii) Common errors were treating potential energy as positive, the use of the wrong radii and the use of mgh. Question 4 (a) (c)(i) Many candidates omitted the area in the formula, and there was some confusion over powers of 10. Very few candidates were able to give a satisfactory reason for the reduced emf when the spring stiffness increased. Of those who mentioned the magnet, most stated that it would move less, seemingly unaware that previously it did not move at all. Well done by most. (c)(ii) Apart from some poor scripts where no scale was attempted, most answers gained at least 2 marks. The commonest errors were to start the graph at 0 instead of 8V and to draw fewer than 3 cycles. Question 5 Most candidates did not attempt to calculate the weight to subtract from the thrust, and hence scored only 1 mark for the use F = mm. (a)(ii) Most answers stated that mass decreases but some did not adequately explain why acceleration increases. The decreasing gravitation field strength was mentioned less often. (a)(iii) Most answers scored either 2 or 0. The many incorrect factors mentioned included pressure, mass and gravity. (a)(iv) Poorly answered. Common incorrect approaches were to use of v = u + aa and most popularly the rocket equation, both of which are blind alleys. (a)(v) Most were convinced that the process was adiabatic and many failed to mention the work done in expansion. Most candidates used the rocket equation correctly and arrived at a ratio of 6.4 or 0.16, but many gave this as the answer, thus gaining only 2 marks. Question 6 Well done, but some failed to square. (a)(ii) Most answered correctly. 4 of 5

5 (c) Many good accounts of how the image is produced were seen and some excellent accounts of the importance of acoustic impedance were offered. However, to gain high marks, both bullet points need to be addressed in some detail, and this was not often seen. Vague statements about the clarity of the image were not accepted for the meaning of resolution, but most candidates were aware of the importance of wavelength. Question 7 (a) (c)(i) Most answer were clearly expressed and gained full marks. Again this was well understood by most candidates. Most candidates gave cladding as the medium with the higher index. (c)(ii) Almost universally correct. (c)(iii) Generally good knowledge of this, but more than reduced quality of image was expected. Question 8 Liquid hydrogen was not accepted as a suitable proton-rich liquid. (a)(ii) Most had a good knowledge, but magnetic field was not mentioned by some candidates, who scored zero. (a)(iii) Most mentioned realignment of the protons but often omitted to explain that the applied field was removed. (a)(iv) Most candidates gained the final mark for describing the variation in the magnetic field caused by a buried object. However, few mentioned that the frequency of the signal was the important measurement. Too many poor answers discussing the gravitational field were seen. Many answers gave the frequency as the important property. Good candidates gained full marks in two concise sentences. 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 5 of 5