2022 AHS Physics Prelim Paper 3

1 Anglican High School 2022_S4_Prelim_PHY_P3 [Turn over CLASS CLASS INDEX 4 Anglican High School 2022_S4_Prelim_PHY_P3 [Turn over 13 September 2022 1 hour 50 minutes This document consists of 12 printed pages and 2 blank pages Anglican High School Secondary Four Preliminary Examination 2022 S4

2 Anglican High School 2022_S4_Prelim_PHY_P3 [Turn over Section A 1 In this experiment, you will investigate the effect of a frictional load on an electric motor. You are provided with: • a 4.5 V power supply, • a small electric motor, • an ammeter, • a voltmeter, • a resistor of resistance 10 Ω, • a switch or plug key, • electrical leads, • a wooden rod, • a piece of Blu-Tack. (a) Set up the circuit shown in Fig. 1.1. Fig. 1.1 Fix the motor to the bench using the piece of Blu-Tack, as shown in Fig. 1.2. Fig. 1.2 (i) With the switch open, record the voltmeter reading V0. V0 = ….………………………………….. [1] (ii) Check that the shaft of the motor is free to spin by rotating it a few times by hand. Close the switch. Record the potential difference V1 across the motor and the current I1 in the circuit. V1 = ….…………………………………….. I1 = ….…………………………………….. [2]

3 Anglican High School 2022_S4_Prelim_PHY_P3 [Turn over (iii) Open the switch. Calculate the input power P1 to the motor using the equation shown. P1 = V1 I1 P1 = ……………………………………… [1] (b) Close the switch. Use the wooden rod to press gently on the shaft of the motor, as shown in Fig. 1.3. Fig. 1.3 Press down on the wooden rod until the shaft just stops spinning. (i) Record the potential difference V2 across the motor and the current I2 when the motor is not spinning. V2 = ….…………………………………….. I2 = ….…………………………………….. [1] Open the switch. (ii) Calculate the resistance R of the motor using the equation shown. R = ……………………………………… [1]

4 Anglican High School 2022_S4_Prelim_PHY_P3 [Turn over (c) Some of the input energy to the motor in (a)(iii) is wasted as thermal energy in the coil of the motor. The proportion Q of the energy wasted in this way is given by the equation shown. Calculate Q. Q = ……………………………………… [1] (d) A student uses the apparatus shown in Fig. 1.4 to determine the minimum force F that the rod exerts on the shaft of the motor to stop it spinning. Fig. 1.4 Describe how F may be determined using the apparatus in Fig. 1.4. …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… …………………………………………………………………………………………………… ………………………………………………………………………………………………… [2] (e) Suggest a change to the apparatus in Fig. 1.4 so that F can be measured directly. ……………………………