NJC H2 Physics Prelim P3 QP

[Turn over NATIONAL JUNIOR COLLEGE SENIOR HIGH 2 PRELIMINARY EXAM Higher 2 CANDIDATE NAME SUBJECT CLASS REGISTRATION NUMBER PHYSICS Paper 3 Longer Structured Questions Candidate answers on the Question Paper. No Additional Materials are required. 9749/03 25 Aug 2023 2 hours READ THESE INSTRUCTION FIRST Write your subject class, registration number and name on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. The use of an approved scientific calculator is expected, where appropriate. Section A Answers all questions. Section B Answer one question only. You are advised to spend one and a half hours on Section A and half an hour on Section B. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A 1 / 7 2 / 10 3 / 9 4 / 10 5 / 8 6 / 6 7 / 10 Section B 8 / 20 9 / 20 Total (80m) This document contains 28 printed pages and 4 blank pages.

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4 Section A 1 A bungee jumper of mass 60 kg is attached to an elastic rope which starts to stretch after a short time of free fall. The gravitational potential energy of the bungee jumper is 0 J when she has fallen through 40 m to the lowest point. (a) gravitational potential energy / kJ elastic potential energy / kJ kinetic energy / kJ top 0 0 half-way 2.6 bottom 0 Fig. 1.1 Fill up the missing energies at the top, bottom and half-way positions in Fig 1.1. Drag forces can be considered negligible. [2] (b) Show that the unstretched length of the elastic rope is 10 m. [2] (c) Determine at what extension will the kinetic energy of the bungee jumper be the highest. extension = ……………………….. m [3] [Total: 7]

5 [Turn over 2 Fig. 2.1 shows a small conducting sphere suspended from a long insulating thread between two metal plates M and M' that are 0.0500 m apart. The plates are connected to a  35.0 10 V battery. The sphere has a radius of 0.0025 m and a mass of 1.0 g. Fig. 2.1 The sphere is given an initial displacement such that the sphere touches M. It then moves rapidly to M', touches it, and returns rapidly to M again. This process repeats itself. (a) State and explain why an initial displacement to touch one of the plates is necessary for the process to start. ……………………………………………………………………………………………………………… ……………………………………………………………………………………………………………… ………………………………………………………………………………………………………... [2] (b) When the sphere touches either plate, it acquires a potential that is equal to the potential difference between the plates. The electrical potential on the surface of a charged conducting sphere can be determined by assuming that all its charges are accumulated at the centre of the sphere. Show that the charge on the sphere when it touches M is 50 o . [1] support M M' long insulating thread 0.0500 m

6 (c) If the electric field between the plates is uniform, calculate the magnitude of the electrostatic force acting on the sphere. force =…………..……….. N [1] (d) As a long thread is used, the motion of the sphere is nearly horizontal and is due to electrostatic force only. Determine the time taken for the sphere to move from M to M'. time taken =………………. s [3] (e) When the battery is removed from Fig. 2.1, the plates remain equally but oppositely charged. The sphere is totally discharged and given an initial displacement to enable it to reach one of the plates. State and explain how the time taken to move from one plate to the other will change. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. …………………………………………………………………………………………………………….. ………………………………………………………………………………………………………… [3] [Total: 10]

7 [Turn over 3 (a) A student wanted to light a lamp, but only had available a 12 V battery of negligible internal resistance. In order to reduce the battery voltage, he connected the circuit as shown in Fig. 3.1. The maximum value of the resistance of the rheostat XY was 1000 Ω. Fig. 3.1 He found that, when the sliding contact P of the rheostat was moved down from X to Y, the voltmeter reading dropped from 12 V to 11 V. Calculate the resistance of the voltmeter. resistance = ............................................ Ω [2] (b) He modified the above circuit into the one shown in Fig. 3.2 below, using the rheostat as a potentiometer, and was now able to adjust the rheostat to give a voltmeter reading of 3.0 V. Fig. 3.2 (i) Calculate the current that flows through the voltmeter. current = ............................................ A [1] X Y A V 12 V P B X Y A B V 12 V P

8 (ii) Assuming that the current in (i) is negligible compared with the current through the rheostat, determine how far down from X the sliding contact P would have been moved. Express your answer as a fraction of the length of XY. fraction of the length of XY = ............................................ [2] (iii) The student then removed the voltmeter in Fig. 3.2 and then connected a lamp rated at 0.60 W, 3.0 V in its place, but it was very dim. By calculating the power delivered to the lamp, explain this observation. ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… ………………………………………………………………………………………………………… …………………………………………………………………………………………………… [4] [Total: 9]

9 [Turn over 4 (a) (i) Explain what is meant by the diffraction of a wave. ………………………………………………………………………………………………………… …………………………………………………………………………………………………… [1] (ii) State an important condition for significant diffraction to occur. …………………………………………………………………………………………………… [1] (b) A diffraction grating with 300 lines per millimeter is being used in a typical light experiment. Different types of light are allowed to fall normally on a diffraction grating and the resultant pattern formed is to be studied. The first light source to be studied is a white light consisting of wavelengths between 400 nm and 700 nm (i) Determine the maximum order of the complete spectrum that can be observed. maximum order = ……………….. [2] (ii) Determine the order of the complete spectrum before the first overlapping between two higher order spectra. order = …………………. [3]

10 (c) The next experiment is of light from a low pressure sodium lamp. Light from the lamp consists mostly of two wavelengths, 588.99 nm and 589.59 nm. (i) Explain quantitatively the problem that would likely arise in observing the spectral lines. ………………………………………………………………………………………………………… …………………………………………………………………………………………………… [2] (ii) Suggest a refinement to the set up to help overcome this problem.