A-level PHYSICS Paper 3 Section B Electronics

Materials For this paper you must have: • a pencil and a ruler • a scientific calculator • a Data and Formulae Booklet • a protractor. Instructions • Use black ink or black ball-point pen. • Fill in the boxes at the top of this page. • Answer all questions. • You must answer the questions in the spaces provided. Do not write outside the box around each page or on blank pages. • If you need extra space for your answer(s), use the lined pages at the end of this book. Write the question number against your answer(s). • Do all rough work in this book. Cross through any work you do not want to be marked. • Show all your working. Information • The marks for questions are shown in brackets. • The maximum mark for this paper is 35. • You are expected to use a scientific calculator where appropriate. • A Data and Formulae Booklet is provided as a loose insert. Please write clearly in block capitals. Centre number Candidate number Surname Forename(s) Candidate signature I declare this is my own work. A-level PHYSICS Paper 3 Section B Electronics Time allowed: The total time for both sections of this paper is 2 hours. You are advised to spend approximately 50 minutes on this section. 2 *02* IB/M/Jun21/7408/3BE Do not write outside the Section B box Answer all questions in this section. 0 1 Figure 1 shows a simplified structure of an N-channel enhancement mode MOSFET. Figure 1 0 1 . 1 State the name of the part shown in this MOSFET structure that causes the input resistance to be very large. [1 mark] 0 1 . 2 Which terminal of the MOSFET is connected directly to 0 V when it is used as a simple switch? Tick () one box. [1 mark] drain gate source 3 *03* Turn over ► IB/M/Jun21/7408/3BE Do not write outside the box Figure 2 shows how the drain–source current IDS of the MOSFET varies with drain–source voltage VDS for a range of gate–source voltages VGS. Figure 2 The MOSFET is used as a simple switch in a filament lamp circuit. The circuit uses power rails of 12 V and 0 V. The resistance of the lamp is 154 Ω when operating at its full power of 0.65 W. 0 1 . 3 Deduce the minimum value of VGS needed for the lamp to operate at full power. [2 marks] VGS = V Question 1 continues on the next page 4 *04* IB/M/Jun21/7408/3BE Do not write outside the box 0 1 . 4 Figure 3 shows an individual MOSFET. The drain–source leakage current IDSS for this MOSFET is about 10 nA. Figure 4 shows a microchip where millions of MOSFETs are combined to enable complex processes to be carried out on one chip. Figure 3 Figure 4 A mobile phone has a central processing unit (CPU) which uses a microchip similar to the one in Figure 4. Table 1 shows the technical specification for the mobile phone. Table 1 Number of transistors in the CPU 8.5 × 109 Battery capacity 3110 mA h Phone time available on stand-by from one full charge ≈ 12 hours A fully charged battery with a capacity of 1 A h allows 3600 C of charge to flow through it before it is fully discharged