2013_PJC_H2_Physics_P3 (Solutions)

1 Answers to 2013 JC2 Preliminary Examination Paper 3 (H2 Physics) Suggested Solutions: No. Solution 1(a)(i) Let t be the time taken for the ball to reach the maximum height. The gradient of the v−t graph gives the acceleration, which is 9.81 m s−2 because the ball is falling freely. 02 59.81 0t   2.5t  s The time taken is 2.5 s. 1(a)(ii) The area under the v−t graph gives the displacement. 1 2.5484 252s   32s  m The maximum height is 32 m. 1(b)(i) 1(b)(ii) The ball will experience air resistance and weight in the same direction. Therefore, the net downward acceleration is larger and the time taken will be shorter to reach a smaller maximum height. 2(a) The principle of superposition states that when two or more travelling waves of the same type meet at a point in space, the resultant displacement at that point is the vector sum of the displacements that the waves would separately produce at that point. velocity / m s−1 t / s 0 25 − 25

2 2(b)(i) Path difference  2  0.020  0.040 m 2(b)(ii) Path difference = 2   2  0.040  0.080 m vf   4000 (0.080)  320 m s−1 2(b)(iii) The sound waves from path LXM and LYM travel in the opposite directions and meet. Since both waves are of equal amplitude, frequency and speed, they superpose and interfere to form a stationary wave. 3(a) Potential difference = 2.0 V 3(b) Using VR I , 2.0 = (1.2  103) I I = 1.67  10−3 A R = 31067.1 0.7  I V = 4200 Ω or 4.2 kΩ 3(c) From Fig. 3.1, light intensity = 24 Wm −2 3(d) Length of strip,     m 060.0100.10100.510 33   Using AR  , 7 24200 5.0 10 3.5 100.060 RA    Ωm 3(e) Larger changes in R at low light intensities, resulting in larger changes in the p.d. across the LDR. Hence greater sensitivity of the LDR at low light conditions, which is used to control the brightness of the lamp.

3 4(a) 4(b)(i) dE dt  0c o sNBA t    20 100 0.35 2.5 10 0.005    175 V The average e.m.f. induced is 175 V. 4(b)(ii) As the coil turns, the flux linkage through the coil decreases. Hence, the induced magnetic field should be in the same direction as the external field. Using right-hand grip rule, the direction of the induced current is clockwise, which means that B is at a higher potential than A. 4(c) The maximum torque on the coil occurs when the plane of the coil is vertical. Maximum torque experienced by the coil, BFd  NB L d NB A   I I 2100 0.35 1.2 2.5 10     1.05 Nm 5(a) Threshold frequency of , refers to the minimum frequency of the illuminating source that will cause a photoelectron to be ejected. 5(b)(i) Energy of a photon,    34 8 19 9 6.63 10 3 10 4.4 1 0 450 1 0 hcE         J e.m.f. / V t / s 0 max.E − max.E 0