2017 Physics. Advanced Higher. Finalised Marking Instructions

Transcription

1 National Qualifications Physics Advanced Higher Finalised Marking Instructions Scottish Qualifications Authority 07 The information in this publication may be reproduced to support SQA qualifications only on a noncommercial basis. If it is reproduced, SQA should be clearly acknowledged as the source. If it is to be used for any other purpose, written permission must be obtained from permissions@sqa.org.uk. Where the publication includes materials from sources other than SQA (secondary copyright), this material should only be reproduced for the purposes of examination or assessment. If it needs to be reproduced for any other purpose it is the centre s responsibility to obtain the necessary copyright clearance. SQA s NQ Assessment team may be able to direct you to the secondary sources. These ing instructions have been prepared by examination teams for use by SQA appointed ers when ing external course assessments. This publication must not be reproduced for commercial or trade purposes.

2 General ing principles for Advanced Higher Physics This information is provided to help you understand the general principles you must apply when ing candidate responses to questions in the paper. These principles must be read in conjunction with the detailed ing instructions, which identify the key features required in candidate responses. (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) Marks for each candidate response must always be assigned in line with these general ing principles and the detailed ing instructions for this assessment. Marking should always be positive. This means that, for each candidate response, s are accumulated for the demonstration of relevant skills, knowledge and understanding: they are not deducted from a maximum on the basis of errors or omissions. If a specific candidate response does not seem to be covered by either the principles or detailed ing instructions, and you are uncertain how to assess it, you must seek guidance from your team leader. There are no half s awarded. Where a wrong answer to part of a question is carried forward and the wrong answer is then used correctly in the following part, the candidate should be given credit for the subsequent part or follow on. Unless a numerical question specifically requires evidence of working to be shown, full s should be awarded for a correct final answer (including units if required) on its own Credit should be given where a diagram or sketch conveys correctly the response required by the question. It will usually require clear and correct labels (or the use of standard symbols). Marks are provided for knowledge of relevant relationships alone, but when a candidate writes down several relationships and does not select the correct one to continue with, for example by substituting values, no can be awarded. Marks should be awarded for non-standard symbols where the symbols are defined and the relationship is correct, or where the substitution shows that the relationship used is correct. This must be clear and unambiguous. Where a triangle type relationship is written down and then not used or used incorrectly, then any for a relationship should not be awarded. Significant figures Data in question is given to significant figures. Correct final answer is 8 6 J Final answer 8 J or 8 58 J or J Award the final. Final answer 8 J or J Do not award the final Candidates should not be credited for a final answer that includes: three or more figures too many or two or more figures too few, ie accept two more or one fewer page

3 (l) The incorrect spelling of technical terms should usually be ignored and candidates should be awarded the relevant, provided that answers can be interpreted and understood without any doubt as to the meaning. Where there is ambiguity, the should not be awarded. Two specific examples of this would be when the candidate uses a term that might be interpreted as reflection, refraction or diffraction (eg defraction ) or one that might be interpreted as either fission or fusion (eg fussion ). (m) Marks are awarded only for a valid response to the question asked. For example, in response to questions that ask candidates to: describe, they must provide a statement or structure of characteristics and/or features; determine or calculate, they must determine a number from given facts, figures or information; estimate, they must determine an approximate value for something; explain, they must relate cause and effect and/or make relationships between things clear; identify, name, give, or state, they need only name or present in brief form; justify, they must give reasons to support their suggestions or conclusions, eg this might be by identifying an appropriate relationship and the effect of changing variables; predict, they must suggest what may happen based on available information; show that, they must use physics [and mathematics] to prove something eg a given value all steps, including the stated answer, must be shown; suggest, they must apply their knowledge and understanding of physics to a new situation. A number of responses are acceptable: s will be awarded for any suggestions that are supported by knowledge and understanding of physics; use your knowledge of physics or aspect of physics to comment on, they must apply their skills, knowledge and understanding to respond appropriately to the problem/situation presented (for example by making a statement of principle(s) involved and/or a relationship or equation, and applying these to respond to the problem/situation). They will be rewarded for the breadth and/or depth of their conceptual understanding. page

4 (n) Marking in calculations Question: The current in a resistor is 5 amperes when the potential difference across it is 7 5 volts. Calculate the resistance of the resistor. ( s) Candidate answer Mark + Comment. V = IR : formula 7 5 = 5R : substitution R = 5 0 Ω : correct answer. 5 0 Ω s: correct answer. 5 0 s: unit missing Ω 0 s: no evidence, wrong answer 5. Ω 0 s: no working or final answer 6. V 75 R 40 I 5 s: arithmetic error V 7. R 40 : formula only I V 8. R : formula only I V 75 R I 5 V 75 R 40 I 5 V 5 R 50 I 75 V 75 R 50 I 5 I 75 R 50 V 5 s: formula & subs, no final answer s: formula & subs, wrong answer : formula but wrong substitution : formula but wrong substitution 0 s: wrong formula 4. V=IR s: formula & subs, arithmetic error 7 5 = 5 R R = 0 Ω 5. V=IR I 5 R 0 V 75 : formula correct but wrong rearrangement of symbols page 4

5 Detailed Marking Instructions for each question. (a) v = 0 4t + t v = (0 4 0 ) + ( 0) v = 0 0 m s - Accept: 0, 0 04, (b) s 0 4t t. dt 04 s t t ( c ) s 0 when t 0, c 0 04 s 0 +0 s 6m Accept: 4, 58, 58 Solution with limits also acceptable..0 s 04 t t. dt 0 04 t s (.0) (0) s s 6m t 0 0 page 5

6 . (a) (i) If centripetal force is included and in the downward direction ignore If centripetal force is included and in any other direction award 0 s Any mention of centrifugal force award 0 s. (ii) If centripetal force is included and in the upward direction ignore. If centripetal force is included and in any other direction award 0 s Any mention of centrifugal force award 0 s. (iii) (A) T + (0 59 8) = 4 0 T = 0 57 N Accept: 0 6, 0 570, (B) T = 7 4 N (b) Accept: 7, 7 4, 7 40 the tension reduces (to zero) Independent s. weight is greater than the central force that would be required for circular motion. (c) Shape 0 48 and for amplitude 0 7(0) time for half cycle Marks independent. page 6

7 . (a) I mr I I 007 kg m Accept: 0 0, 0 068, (b) (i) T Fr T T N m Accept: 0 06, , (ii) T I Or consistent with (a) and (b)(i) 5 rads Accept: 4, 5, 59 (iii) s r rads Accept: 0, 5, Or consistent with (a), (b)(i) and (b)(ii) 0 0t t and t (c) I mr I cube cube 5 0 (0 0 ) 5 Or consistent with (a) I ( I I ) cube 007 (007 (5 0 (0 0 ) )) rads Accept: 0,, 0 page 7

8 4. (a) (i) mv F r 4 v 5ms ( ) 40 v SHOW question mv r v v GMm r GM r v 5 ms If final answer not shown a maximum of can be awarded. (ii) v c r T 5 T ( ) s T Accept: 4 4, 4 89, (b) (i) The work done in moving unit mass from infinity (to that point). (ii) 4 4 Vlow Vhigh V low V 9 0 high E E E Vm J Accept: 4, 9, Can also be done by calculating potential energy in each orbit and subtracting. for relationship for all substitutions for subtraction for final answer including unit page 8

9 5. Demonstrates no understanding 0 s Demonstrates limited understanding s Demonstrates reasonable understanding s Demonstrates good understanding s This is an open-ended question. Open-ended question: a variety of physics arguments can be used to answer this question. Marks are awarded on the basis of whether the answer overall demonstrates no, limited, reasonable or good understanding. : The student has demonstrated a limited understanding of the physics involved. The student has made some statement(s) which is/are relevant to the situation, showing that at least a little of the physics within the problem is understood. s: The student has demonstrated a reasonable understanding of the physics involved. The student makes some statement(s) which is/are relevant to the situation, showing that the problem is understood. s: The maximum available would be awarded to a student who has demonstrated a good understanding of the physics involved. The student shows a good comprehension of the physics of the situation and has provided a logically correct answer to the question posed. This type of response might include a statement of the principles involved, a relationship or an equation, and the application of these to respond to the problem. This does not mean the answer has to be what might be termed an excellent answer or a complete one. page 9

10 6. (a) (electron) neutrino () and positron () e and acceptable (b) (i) Correctly ed (ii) (White) Dwarf Or consistent with (b)(i) (iii) L L b= 4r r 7 r 0 m Accept:, 08, (c) L M 5 L M L 0 5 L 5 L 560 L0 Accept: 500, page 0

11 7. (a) Atoms in the Nd:YAG have a shorter lifetime (in the excited state) OR Atoms in the Ar have a longer lifetime (in the excited state) f E and t E or t f (b) (i) h Et 4 6 E(min) 50 0 E (min) 9 0 J Accept:, 06, (ii) ( ) E h( ) f ( ) 4 ( ) f 7 0 Hz Accept:, 66, 659 f Or consistent with (b)(i) page

12 8. (a) At t=0 sin t 0, which would mean that y=0. This is not the case in the example here, where y=a at t=0 Accept assumptions that no energy is lost (b) (i) F ( ) m y ( ) ky ky my k m f f f k m k m (ii) f T 080 f k m k k N m - Accept: 0, 0 8, 0 84 (iii) 080 T T 057 s Accept: 0 6, 0 566, k f and T= m f 050 T T 056 s Accept: 0 6, 0 564, Or consistent with (b)(ii) page

13 (c) () s all three correct () for two correct page

14 9 (a) (i) f 9 f f 47 Hz (ii) 450 v f 4 v v 05 ms - Accept:0, 05, 05 5 (iii) E ka E E (950 0 ) 8 A A m E A A E acceptable Accept: 4, 59, 588 (b) T v 0 T T 540 N Accept: 500, 58, 57 5 (c) (i) Waves reflected from each end interfere (to create maxima and minima). (ii) f Hz page 4

15 0. (a) Pattern produced by interference. Slits horizontal and vertical or at right angles (b) The spots are closer together. The green light has a shorter wavelength and since dsin m, d is fixed, (sin) is smaller. An argument quoting Young s slits is also acceptable. D x d is less, D and d are fixed, so x is less page 5

16 (c) (i) D x d m Accept: 7, 6 57, 6 57 (ii) % Uncertainty in fringe separation % % Uncertainty in slit separation % 5 % Uncertainty in slit-screen separation % (can be ignored) % uncertainty in wavelength % % m 7 (iii) Increasing the slit screen distance spreads out the fringes, reducing the (percentage) uncertainty in the fringe separation (which is the dominant uncertainty). page 6

17 (a) Force acting per unit positive charge (in an electric field) (b) (i) Q E 4 r E E E total total N C If value for ε 0 not substituted, max. third line can be done by trigonometry rather than Pythagoras sin 45 9 E total If the final line is not shown then maximum s can be awarded. (ii) F QE F F 67 0 N Accept: 7, 6 65, QQ F and F F F 40r F F 67 0 N Accept: 7, 6 7, 6 7 Accept: 6 78 for (iii) Towards top of page (iv) r 0 0 QQ F 4 0r Q Q 0 C Accept:,, 9 4 Or consistent with (b)(ii). page 7

18 (a) Towards the top of the page. (b) (c) F qvb v 5 0 v 7 0 m s Accept:, 74, 79 (Since F =Bqv) At lower speeds the magnetic force is reduced. Starting with E F v and E B Q is acceptable Second dependant on the first. (d) Therefore unbalanced force (or acceleration) down Or The magnetic force is less than the electric force (All undeflected ions travel at) 7 x 0 5 m s - relative size of forces is independent of mass and of charge. Or consistent with (b) Must justify E v as E & B remain constant B v must also remain constant. page 8

19 . (a) t RC t t s (b) (i) circuit diagram showing (V) d.c. supply, resistor and capacitor all in series. (ii) (A) Values not required. Voltmeter or CRO connected across the capacitor. (After time constant or 000 s) V= 7 6 (V) V V c s V V c s 76 6% (ii) (B) page 9

20 (c) Demonstrates no understanding 0 s Demonstrates limited understanding s Demonstrates reasonable understanding s Demonstrates good understanding s This is an open-ended question. : The student has demonstrated a limited understanding of the physics involved. The student has made some statement(s) which is/are relevant to the situation, showing that at least a little of the physics within the problem is understood. s: The student has demonstrated a reasonable understanding of the physics involved. The student makes some statement(s) which is/are relevant to the situation, showing that the problem is understood. s: The maximum available would be awarded to a student who has demonstrated a good understanding of the physics involved. The student shows a good comprehension of the physics of the situation and has provided a logically correct answer to the question posed. This type of response might include a statement of the principles involved, a relationship or an equation, and the application of these to respond to the problem. This does not mean the answer has to be what might be termed an excellent answer or a complete one. Open-ended question: a variety of physics arguments can be used to answer this question. Marks are awarded on the basis of whether the answer overall demonstrates no, limited, reasonable or good understanding. page 0

21 Mark Additional Guidance 4. (a) (i) Capacitor has low reactance/impedance for high frequencies (therefore more current (and power) will be delivered to the tweeter at high frequencies). (ii) Inductor has low reactance/impedance for low frequencies (therefore more current (and power) will be delivered to the woofer at low frequencies). (b) X fl L L H Accept: 4, 4 4, 4 44 L (c) (i) di dt 00 di L dt 4 90 L 00 L 045 H Accept: 0 5, 0 450, (ii) large (back) EMF. (explanation of rapidly collapsing magnetic field) inducing high voltage Explanation in terms of energy released from inductor is acceptable. [END OF MARKING INSTRUCTIONS] page