A-level PHYSICS Paper 3 Section A

aterials 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 45. • 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 A Time allowed: The total time for both sections of this paper is 2 hours. You are advised to spend approximately 70 minutes on this section. 2 *02* IB/M/Jun21/7408/3A Do not write outside the Section A box Answer all questions in this section. 0 1 Figure 1 shows apparatus used to investigate the inverse-square law for gamma radiation. Figure 1 3 *03* Turn over ► IB/M/Jun21/7408/3A Do not write outside the A sealed source that emits gamma radiation is held in a socket attached to clamp B box . The vertical distance between the open end of the source and the bench is 138 mm. A radiation detector, positioned vertically above the source, is attached to clamp T. A student is told not to move the stands closer together. 0 1 . 1 Describe a procedure for the student to find the value of d, the vertical distance between the open end of the source and the radiation detector. In your answer, annotate Figure 1 to show how a set-square can be used in this procedure. [2 marks] Question 1 continues on the next page 4 *04* IB/M/Jun21/7408/3A Do not write outside the 0 1 box . 2 Before the source was brought into the room, a background count Cb was recorded. Cb = 630 counts in 15 minutes With the source and detector in the positions shown in Figure 1, d = 530 mm. Separate counts C1, C2 and C3 are recorded. C1 = 90 counts in 100 s C2 = 117 counts in 100 s C3 = 102 counts in 100 s RC is the mean count rate corrected for background radiation. Show that when d = 530 mm, RC is about 0.3 s−1 . [2 marks]