2016 Assessment Report Page 1 of 4

2016 ASSESSMENT REPORT

Physics Course Code: PHY415115 The paper was generally well accepted and had some good discriminating questions, allowing students to display their level of expertise. The length of the paper appeared to be correct, as there was little evidence of candidates not completing the paper. The usual problems with significant figures and units on answers, as well as directions where appropriate, occurred. These issues, as usual, were more pronounced for weaker students whom can least afford to lose marks in this way. From experience, if the teacher is very hard on these issues when marking work during the year, even weak students can be trained by the end of the year. It was a concern that, even though candidates were often asked to support their answer with a diagram, a significant number did not. In other instances where a diagram would have helped to clarify the situation, one was not drawn and the answers given were incorrect. The message here is that sketch diagrams are basic to problem solving in Physics. This year Booklet 2 was found to be the most demanding by the candidates, suggesting more emphasis needs to be made on the teaching of this criterion in the future.

Part 1 – Criterion 5 Question 1

This question, which tested a student’s understanding of centripetal acceleration combined with gravitational acceleration, was well attempted by most students but only a few obtained full marks. The answer to Part (a) was west (towards the centre) but full marks were given to many alternative answers, provided a diagram of the situation was included. Part (b) was well answered, as was Part (c)(i). However, Part (c)(ii) was poorly answered. Most students did not realize that this required vector addition of the Fc and Fg forces and hence few students scored any marks. Question 2

Part (a) required an indication of the vector components and a net force. Most included the frictional and normal forces, thus gaining one mark, but received no more when they mistakenly labeled the forward force provided by the train engine as the net force. Many students obtained full marks for the relatively difficult Part (b). It was pleasing to see students calculating the two force components and adding them to provide the answer. However, many students failed to realize that power (in Part (c)) could be calculated by multiplying force by velocity. For the 40% who answered Part (d), many incorrectly subtracted the two forces. Part (e) was well answered by those who attempted it. Question 3

Parts (a) and (b) were well answered, although directions were often omitted. Parts (c) and (d), on the other hand, were more challenging. The meaning of the word component seemed to be a problem for many students, making Part (c) impossible for them to answer. Interestingly, many students correctly calculated the momentum of the pin as their answer to Part (c) but never gave the value of the North-South component.

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Question 4

The numerical parts to this question were well done. On the other hand, the two descriptive parts were a disaster even though they were set pieces that have appeared regularly on past papers! Question 5

This question was a saviour for many students as they were able to score full marks on it. The most common error was the omission of the minus sign in the final calculation of the height of the ball as it reached the mountain.

Part 2 – Criterion 6 Question 6

(a) The most common error is that students think that stronger field means more field lines; and do not understand density of field lines. One student demonstrated that the field is stronger between the wires. Is a group of students being incorrectly taught to draw field lines with disconnected arcs? We hope not!

(b) Many students did not use the appropriate formula from their information sheet. They tried to calculate field due to one wire, then apply it to the other, but commonly used the same current twice.

(c) Many decided the fields would cancel, and forgot about their diagram. Question 7

(a) Well done. (b) The most outstanding issue was the inability to predict the direction of the electric field strength, and draw a

vector diagram. Few students understand a bearing (eg N18.4°E). (c) Very few (3 or 4) knew that the field would be identical. The question was ambiguous. Some students

thought the conductor was uncharged. Only 3 or 4 predicted the induced charge on the conductor due to the charge at S. Marks were given for good reasoning, even if it lead to the wrong conclusion.

Question 8

This question was well done. Question 9

(a) A difficult question. Virtually no candidates managed to do all four parts correctly. (b) Some candidates were incorrectly equating electric field strength, E, with energy, E. Question 10

(a) Generally well done, although many candidates did not relate their explanations explicitly to the radius of the path.

(b) Many did not interpret the 2+ charge correctly, simply calling it +2 coulombs. (c) Disturbingly few candidates did this basic question correctly. (d) Not well done. Most candidates addressed either the reason for the velocity filter, or the principle on which

it works. Few addressed both. Some simply restated the information given in the introduction to the question (zero marks).

Question 11

(a & b) Well done. (c) Those who realised that the back emf was 10 V did this well. A large number of candidates incorrectly

interpreted the emf as the force from Part (b). (d) Poorly done.

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Question 12

(a) Poorly done. Most candidates wrote about Lenz’s Law without saying what the actual cause of the current was. Fewer still were able to correctly relate the induced current to the retarding force.

(b) Very poorly done. (c) Poorly done. Most tried to say why eddy currents are not induced, without answering the question that was

asked. Answers referring to a separation of charge scored best.

Part 3 – Criterion 7 Question 13

(a) Generally well done. (b) (i) Most students drew the emerging ray correctly. (ii) About half of the candidates accurately answered this question. The most common error was not

recognising that the blue ray would be refracted on entering the prism, not just on exiting the prism. (iii) This question was not answered well and many students were confused by the relationship between

refractive indices, the effect on refraction and the effect on the angles when light was entering and leaving the prism.

Question 14

(a) Generally well done. (b) Most students recognised that the frequency remains unchanged in (i) and were able to calculate the relative

refractive index in (ii), with the most common error being the use of an incorrect ratio. (c) Most students correctly drew refracted waves at the boundary, with only a few receiving full marks for also

drawing reflected wave fronts. (d) This question was not well answered by most students. Many drew wave fronts rather than rays, as asked in

the question. Most students were challenged in drawing a neat, accurate diagram. Question 15

(a) (i) Generally well done. (ii) Not done well, with most students not recognising that the second overtone was equivalent to the third

harmonic. (b) (i) Well done, with most students recognising the question related to beat frequency. (ii) Only a few students were able to answer this question correctly. (iii) Many students did not attempt this question. Of those that did, most were able to present an answer. A

significant proportion of students did not recognise that a lower mass would produce a lower frequency and it was this lower frequency from earlier in the question that was required in the calculation.

Question 16

Generally well done. However, many students failed to realise that the first node is ¼ wavelength from an open end and that the distance between nodes is ½ wavelength. Question 17

Whilst there was a wide range of marks for this question, few students gained full marks. Many answers were vague, but credit was given for some evidence of understanding the processes involved. In Part (c), few candidates answered the question specifically as asked - referring to the phase change and zero path difference. Question 18

(a) Most knew how to do the calculation, but lost a half mark because they did not give the answer to 3 sig figs as required when doing a "show that" question.

(b) Generally done well, but quite a few could not handle the powers of 10 properly. (c) This was not well done. For 2 marks the marking examiner expected a diagram (as requested) with the

spectral colours and a clear indication of which colours underwent more deviation.

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Part 4 – Criterion 8 Question 19

(a) (i) Poorly done. Clearly, students were unsure of the work associated with Rutherford and the full range of models from the plum pudding to the standing wave model was suggested.

(ii) Satisfactorily done. Much was written about discrete energy levels, but the relation to the hydrogen spectrum was often missed.

(b) (i) Adequately done. (ii) Well done. Most found the energy, but some lost a mark for not indicating the electron transition. Question 20

(a) Adequately done. Most candidates came up with at least one correct answer. (b) Well done. A common error was using wrong number for ‘run’. (c) Well done. (d) A common error was the wrong slope or wrong threshold frequency. Question 21

(a) This straightforward question was very well answered. (b) Full marks were given for two alternative answers to this question. A consideration of energy gave 2.32 x 10-

14 J (the correct answer), and a consideration of momentum gave 3.03 x 10-15 J. (This approach relied on guessing the directions of the particles after the collision.)

(c) Well done. 6.50 x 1011 m was a common incorrect response. Question 22

Well done generally. Good comments on pellet vs oral. Numerical calculations were competently done. Question 23

Extremely poorly done especially Parts (b) and (c). Students failed to address the question in Part (c). Question 24

Quite well done with most able to carry out the calculation of Part (c). Most students remembered the antineutrino in the decay.