2013 PJC H2 Physics P3

2013/PJC/PHYSICS/9646 [Turn over PIONEER JUNIOR COLLEGE JC2 Preliminary Examination PHYSICS 9646/03 Higher 2 Paper 3 Longer Structured Questions 24 September 2013 2 hours Candidates answer on the Question Paper. No Additional Materials are required. READ THESE INSTRUCTIONS FIRST Write your name, class and index number on all the work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. Section A Answer all questions. Section B Answer any two questions. You are advised to spend about one hour on each section. 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. This document consists of 23 printed pages. Name Class Index Number For Examiner’s Use 1 / 8 2 / 8 3 / 8 4 / 8 5 / 8 6 / 20 7 / 20 8 / 20 Total / 80

2 2013/PJC/PHYSICS/9646 Data speed of light in free space, 81000.3 c ms–1 permeability of free space, 7 0 104   Hm–1 permittivity of free space, 12 0 1085.8  Fm–1    910361   Fm–1 elementary charge, 191060.1 e C the Planck constant, 341063.6 h Js unified atomic mass constant, 271066.1 u kg rest mass of electron, 311011.9 em kg rest mass of proton, 271067.1 pm kg molar gas constant, 31.8R JK–1 mol–1 the Avogadro constant, 231002.6 AN mol–1 the Boltzmann constant, 231038.1 k JK–1 gravitational constant, 111067.6 G Nm2 kg–2 acceleration of free fall, 81 .9g ms–2

3 2013/PJC/PHYSICS/9646 [Turn over Formulae uniformly accelerated motion, 2 2 1 atuts  asuv 222  work done on/by a gas, VpW  hydrostatic pressure, ghp  gravitational potential, r Gm displacement of particle in s.h.m., txx sin0 velocity of particle in s.h.m., tvv cos0 22 0 xx   mean kinetic energy of a molecule kTE 2 3 of an ideal gas, resistors in series, ... 21  RRR resistors in parallel, ... /1/1/1 21  RRR electric potential, r QV 04 alternating current/voltage, txx sin0 transmission coefficient,  kdT 2exp  where   2 28 h EUmk   radioactive decay, ) exp( 0 txx  decay constant, 2 1 693.0 t

4 2013/PJC/PHYSICS/9646 Section A Answer all questions in this section. 1 A ball is thrown vertically upwards with a velocity of 25 m s −1 from ground level and then falls back to its starting point. Fig. 1.1 shows the variation with time of the velocity of the ball. Fig. 1.1 (a) Use Fig. 1.1 to determine (i) the time taken by the ball to reach the maximum height, time = ........................................ s [2] (ii) the maximum height reached by the ball. height = ........................................ m [1] velocity / m s−1 t / s 0 25 − 25

5 2013/PJC/PHYSICS/9646 [Turn over (b) (i) On Fig. 1.1, sketch a graph of the motion of the ball if air resistance is not negligible. [2] (ii) Explain clearly how your answers in (a) will change. ............................................................................................................................. ..... ............................................................................................................................. ..... ............................................................................................................................. ..... ........................................................................................................................... [3]

6 2013/PJC/PHYSICS/9646 2 (a) State the principle of superposition. .............................................................................................................................. .......... .............................................................................................................................. .......... .............................................................................................................................. ... [2] (b) Sound produced by the loudspeaker shown in Fig. 2.1 has a frequency of 34.0 10 Hz. The sound waves arrive at the microphone M via two different paths, LXM and LYM. The left-tube is fixed in position, while the right-tube is a sliding-section. At position M, the sound waves from the two paths interfere. Fig. 2.1 Initially, the lengths of paths LXM and LYM are equal. The sliding-section is then pulled out horizontally to the right by a distance of 0.020 m, and the loudness at microphone M changes from a maximum to a minimum. (i) Determine the path difference between the two waves after the sliding-section is pulled out. path difference = ........................................ m [1] sliding-section which can be moved horizontally X Y loudspeaker microphone L M

7 2013/PJC/PHYSICS/9646 [Turn over (ii) Calculate the speed at which sound travels through the tubes. speed = ........................................ ms −1 [2] (iii) When the opening at M is sealed, explain why a standing wave can be set up in the tube. ............................................................................................................................. ..... ............................................................................................................................. ..... ............................................................................................................................. ..... ............................................................................................................................. ..... ........................................................................................................................... [ 3]

8 2013/PJC/PHYSICS/9646 3 Fig. 3.1 shows how the resistance of a light-dependent resistor (LDR) varies with the intensity of the light incident on it. Fig. 3.1 Fig. 3.2 shows a light-sensing potential divider circuit used in a lamp where the potential difference across the LDR can be used to control the brightness of the lamp in a room. Fig. 3.2 The battery has an e.m.f. of 9.0 V and negligible internal resistance. The 1.2 kΩ resistor is made of carbon. When the room is in a low-light condition, the potential difference across the LDR reaches 7.0 V. (a) State the potential difference across the 1.2 k Ω resistor, when the room is in a low-light condition. potential difference = ........................................ V [1] resistance / kΩ incident light intensity / Wm −2 p.d. to control brightness of lamp 1.2 kΩ 9.0 V

9 2013/PJC/PHYSICS/9646 [Turn over (b) Hence, calculate the resistance R of the LDR. R = ........................................ kΩ [2] (c) Use Fig. 3.1 to determine the light intensity when the p.d. across the LDR is 7.0 V. light intensity = ........................................ Wm −2 [1] (d) Fig. 3.3 shows a close-up of the LDR device used in the circuit in Fig. 3.2. The LDR consists of a uniform strip of semiconductor whose resistance is dependent on the intensity of