2023 AQA A-level PHYSICS 7408/3BB Paper 3 Section B Medical Physics Question Paper & Mark scheme (Merged) June 2023 [VERIFIED]

2023 AQA A-level PHYSICS 7408/3BB Paper 3 Section B Medical Physics Question Paper & Mark scheme (Merged) June 2023 [VERIFIED] A-level PHYSICS Paper 3 Section B Medical physics Thursday 15 June 2023 Morning Time allowed: The total time for Materials both sections of this paper is For this paper you must have: 2 hours. You are advised to • a pencil and a ruler spend approximately • a scientific calculator 50 minutes on this section. • a Data and Formulae Booklet • a protractor. For Examiner’s Use Instructions • Use black ink or black ball-point pen. Question Mark • Fill in the boxes at the top of this page. 1 • Answer all questions. 2 • You must answer the questions in the spaces provided. Do not write 3 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 4 this book. Write the question number against your answer(s). 5 • Do all rough work in this book. Cross through any work you do not want TOTAL 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. *JUN2374083BB01* IB/M/Jun23/E7 7408/3BB 2 Section B Answer all questions in this section. 0 1Brachytherapy is used to treat small tumours. In this technique a sealed radioactive source is placed inside a patient’s body next to the tumour. Explain one advantage of using beta radiation rather than gamma radiation in brachytherapy. [2 marks] Do not write outside the box 2 *02* IB/M/Jun23/7408/3BB 3 0 2Electrophoretic screens are used in handheld electronic devices. The screen contains individual squares known as pixels. Pixels can be changed independently from light to dark to create the shapes of letters and numbers. An external light source is needed in order to read the screen. Figure 1 shows a letter formed by three electrophoretic screens that have different pixel line densities. Pixel line density is the number of pixels along a 1.0 cm length of the screen. Figure 1 0 2 . 1 A particular screen is designed so that two dark pixels separated by one light pixel cannot be resolved as separate images by the eye when viewed from a distance of 0.50 m. Determine, in pixels per cm, the minimum pixel line density required for this screen. typical diameter of cones in a human eye at the fovea = 1.5 μm typical length of the human eye = 21 mm [3 marks] pixels per cm = Question 2 continues on the next page Turn over ► *03* Do not write outside the box IB/M/Jun23/7408/3BB 4 0 2 . 2 On a different electrophoretic screen, two dark pixels separated by one light pixel can just be resolved at a particular distance when the external light source is bright. Explain why these pixels cannot be resolved at the same distance when the intensity of the external light source is reduced.