2022 NYGH Phy Prelims Ans

NANYANG GIRLS’ HIGH SCHOOL ANSWERS Preliminary Examination 2022 Physics SIP Secondary Four Paper 1 1 A 2 B 3 C 4 D 5D 6B 7B 8A 9 C 10 B 11 B 12 B 13 C 14 A 15 C 16 B 17 D 18 B 19 A 20 D 21 C 22 A 23 A 24 D 25 A 26 C 27 D 28 D 29 B 30 B 31 B 32 C 33 B 34 C 35 C 36 A 37 D 38 D 39 B 40 A Paper 2 Question Answer 1 (a) [1] (b) correct arrangement of vectors [1] C 1 = 20.2N [1] C2 = 10.6 N [1] 2 (a) change in velocity per unit time is constant [1] ( b ) [1] for correct shape, [1] for correct values ( c ) (i) Area under graph (allow e.c.f.) = ½(9.0 + 5.0)s x (2.4) m/s [1] = 17 m [1] (ii) total distance / total time = 16.8 m / 9.0 s = 1.9 m/s [1] ( d ) gh = ½ v2 10 m/s2 x (7.0 m – 4.0 m) = ½ v2 [1] v = 7.7 m/s [1] ceiling 110 °100 ° block C2 C1 tension tension weight speed m/s time s 2.0 2.0 4.0 C2 C1 30 N 6.0 8.0 150 ° 20 ° 10 °

Physics SIP 3 (a) Volume = m / d = 86.4 g/2.7 g/cm3 = 32 cm3 [1] Final reading = 40 + 32 = 72 cm3 [1] ( b ) density will be lower [1] 4 (a) F x 8.0 m = 2000 N x 2.0 m [1] F = 500 N [1] ( b ) The force will decrease as the perpendicular distance of F from A increases [1]. The moment due to the weight will decrease. [1] 5 (a) The water particles move/vibrate perpendicular to the direction of the water wave. [1] ( b ) ( i ) 6.0 m / 4 = 1.5 m [1] ( i i ) 5 / 12.5 = 0.40 Hz [1] ( i i i ) v = 0.40 Hz x 1.5 m [1] = 0.60 m/s [1] 6 (a) volume of fixed mass of liquid [1] ( b ) (28 °C - 0 °C) / (40 °C - 0 °C) = (TL - 0 °C) / (50 °C - 0 °C) [1] ( c ) Thermal energy is used to increase spacing between molecules in the liquid state to change it into vapour state. Potential energy in the molecules increase. [1] No change in K.E. which determines the temperature. [1] [1]

7 8 (a) metal sphere induced to have negative charges closer to A and positive charges closer to B. [1] Unlike charges attract. [1] ( b ) I = Q/t Q = 30 000 A x 0.20 s [1] = 6 000 C [1] 9 (a) e.m.f. is the work done to move 1 coulomb of charge around the entire circuit. [1] ( b ) ( i ) 18 Ω + (1/30 Ω + 1/20 Ω)-1 [1] = 30 Ω [1] ( i i ) p.d. = 12 V / 30 Ω × 12 Ω [1] = 4.8 V [1] ( i i i ) current = 4.8 V / 20 Ω [1] = 0.24 A [1] ( c ) LP / 2A : LQ / 3A = 18 Ω : 30 Ω [1] LP : LQ = 6 : 15 = 2 : 5 [1] 10 (a) current flows from A to B [1] ( b ) (i) split ring commutator [1] (ii) Y reverses the direction of the current in the coil every ½ cycle [1] when the coil passes the vertical position so that the forces are reversed [1] R [1] [1] [1] [1] F E

Physics SIP 11 (a) Sound wave with frequency higher than 20 000 Hz. [1] ( b ) Ultrasound cannot be heard / less easily dispersed / transmitted with less energy loss compared to sound. [1] ( c ) ( i ) 170 ms [1] ( i i ) time taken to receive reflected s ignal is longer [1] for vacant lots as the distance travelled is longer [1] amplitude of signal is smaller as there is greater energy loss for longer distance travelled for vacant lots [1] ( i i i ) 340 m s-1 x (20 x 10-3) s ൊ 2 [1] = 3.4 m [1] ( i v ) Time taken between transmission and reception of signals is shorter. OR The amplitude is smaller. ( d ) Presence of wind may carry away the wave and hence the wave cannot be detected by the receiver. 12 (a) horizontal arrows [1] both arrows point towards S-pole [1] ( b ) ( i ) Current flowing in the circuit will magnetise iron core.[1] Armature induced to form an unlike pole and is attracted to iron core. [1] Armature rotates clockwise and contacts are pushed up to close secondary circuit. [1] ( i i ) soft iron [1], easily magnetised and easily demagnetized. [1] ( i i i ) operator does not have to be physically close to a secondary ci rcuit with high current/operating dangerous machines.[1] ( i v ) complete the circuit [1] north pole set up as shown [1]

13 E (a) infra-red radiation [1] ( b ) reflects heat/radiation down to food, which cooks faster OR reflects heat away from outer metal case, which does not get hot. [1] ( c ) ( i ) live wire: 230 V, 8.3 A neutral wire: 0 V, 8.3 A earth wire: 0 V, 0 A all current correct [1], all voltage [1] OR more than 3 items correct [1] (ii) Earth wire is connected to metal case. [1] When metal case becomes live, current is directed to earth and not user who touches it. [1] (iii) P = IV = 8.3 A x 230 V [1] = 1900 W [1] ( i v ) The heating element temperature will be lower OR other effects due to lower temperature e.g. longer cooking time or food not properly cooked. [1] 13 O (a) (i) current going right to left [1] (ii) rings around the iron ring [1] direction of field anti-clockwise [1] (iii) X is a South pole. [1] ( b ) ( i ) When switch is closed, coil S experiences increasing magnetic flux. [1] By Faraday’s Law, an emf is set up in coil S which then drives a current through the galvanometer.[1] (ii) There is a deflection in the opposite direction. [1] Coil S experiences decreasing magnetic flux when the switch is opened. [1] (iii) use d.c. source with larger emf [1], increase number of turns in coil S [1]