A-level PHYSICS 7408/3BE Paper 3 Section B Electronics[DOWNLOAD TO PASS]

MARK SCHEME – A-LEVEL PHYSICS – 7408/3BE – JUNE 2021 5 answer should be quoted to 3 sf. An answer to 1 sf will not normally be acceptable, unless the answer is an integer eg a number of objects. In non-practical sections, the need for a consideration will be indicated in the question by the use of ‘Give your answer to an appropriate number of significant figures’. 3.9 Unit penalties An A-level paper may contain up to 2 marks (1 mark for AS) that are contingent on the candidate quoting the correct unit for the answer to a calculation. The need for a unit to be quoted will be indicated in the question by the use of ‘State an appropriate SI unit for your answer’. Unit answers will be expected to appear in the most commonly agreed form for the calculation concerned; strings of fundamental (base) units would not. For example, 1 tesla and 1 Wb m–2 would both be acceptable units for magnetic flux density but 1 kg m2 s–2 A–1 would not. 3.10 Level of response marking instructions Level of response mark schemes are broken down into three levels, each of which has a descriptor. The descriptor for the level shows the average performance for the level. There are two marks in each level. Before you apply the mark scheme to a student’s answer read through the answer and annotate it (as instructed) to show the qualities that are being looked for. You can then apply the mark scheme. Determining a level Start at the lowest level of the mark scheme and use it as a ladder to see whether the answer meets the descriptor for that level. The descriptor for the level indicates the different qualities that might be seen in the student’s answer for that level. If it meets the lowest level then go to the next one and decide if it meets this level, and so on, until you have a match between the level descriptor and the answer. With practice and familiarity you will find that for better answers you will be able to quickly skip through the lower levels of the mark scheme. When assigning a level you should look at the overall quality of the answer and not look to pick holes in small and specific parts of the answer where the student has not performed quite as well as the rest. If the answer covers different aspects of different levels of the mark scheme you should use a best fit approach for defining the level and then use the variability of the response to help decide the mark within the level. i.e. if the response is predominantly level 2 with a small amount of level 3 material it would be placed in level 2. The exemplar materials used during standardisation will help you to determine the appropriate level. There will be an answer in the standardising materials which will correspond with each level of the mark scheme. This answer will have been awarded a mark by the Lead Examiner. You can compare the student’s answer with the example to determine if it is the same standard, better or worse than the example. You can then use this to allocate a mark for the answer based on the Lead Examiner’s mark on the example. You may well need to read back through the answer as you apply the mark scheme to clarify points and assure yourself that the level and the mark are appropriate. Indicative content in the mark scheme is provided as a guide for examiners. It is not intended to be exhaustive and you must credit other valid points. Students do not have to cover all of the points mentioned in the indicative content to reach the highest level of the mark scheme. An answer which contains nothing of relevance to the question must be awarded no marks. MARK SCHEME – A-LEVEL PHYSICS – 7408/3BE – JUNE 2021 6 Question Answers Additional comments/Guidelines Mark AO 01.1 Silicon dioxide layer Accept Silicon dioxide 1 AO1 1a Question Answers Additional comments/Guidelines Mark AO 01.2 drain gate source 1 AO1 1a Question Answers Additional comments/Guidelines Mark AO 01.3 For lamp P = I 2 R I = √(P/R) = √(0.65 W / 154 Ω) = 65 mA 1 This leads to a voltage across the lamp of approx 10 V and a VDS of approx 2 V Read from graph to give VGS = 3.4 V 2 Must use P = I 2 R Accept a VGS range of 3.3 V to 3.5 V 2 AO2 1b AO3 1b MARK SCHEME – A-LEVEL PHYSICS – 7408/3BE – JUNE 2021 7 Question Answers Additional comments/Guidelines Mark AO 01.4 Current consumption on stand-by: 8.5 × 109 × 10 × 10–9 = 85 A Makes a meaningful calculation (one which 3 AO2 1b 1 can lead to a conclusion) using data for the CPU. AO2 1b AO3 1a Makes a meaningful calculation (one which Battery life: 3600 C × 3.110 = 1.12 × 104 C 2 can lead to a conclusion) using data for battery. Use 1.12 × 104 = 85 × t Uses the value of t to reach a valid conclusion Gives t = 131.8 seconds (accept 132 seconds OR just over 2 mins) which is much less than 12 hours 3 OR Uses the values of the currents from the CPU and battery to reach a valid conclusion Total 7 MARK SCHEME – A-LEVEL PHYSICS – 7408/3BE – JUNE 2021 8 Question Answers Additional comments/Guidelines Mark AO 02.1 All Q states correct for 1 mark 1 AO3 1a Question Answers Additional comments/Guidelines Mark AO 02.2 9 V X 0 V Correct orientation for resistor & switch Correct tap-off point for X 2 AO3 2a AO3 2a Inputs Output C B A Q 0 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0 1 0 0 1 1 0 1 0 1 1 0 1 1 1 1 1 MARK SCHEME – A-LEVEL PHYSICS – 7408/3BE – JUNE 2021 9 Question Answers Additional comments/Guidelines Mark AO 02.3 Q =