In this experiment you will investigate a light dependent resistor (LDR). You are provided with: • a power supply • a switch • a voltmeter with two leads that may be connected between different points in the circuit • a light dependent resistor (LDR) • a 560 Ω resistor • a piece of card. The supervisor has constructed a series circuit consisting of the power supply, the LDR, the resistor and the switch. The circuit has three points labelled P, Q and S.

1. (a)Draw a diagram of the circuit arrangement using the correct symbols for the components in the circuit. Choose from the symbols shown in Fig. 1.1. You do not need to label points P, Q and S on your diagram.[2]
2. (b)(i)Connect the voltmeter across the LDR between points P and Q. Close the switch. Record VPQ, the voltmeter reading across P and Q. This is VPQ under normal lighting conditions. VPQ = ..................................................... V [1] Open the switch.[1]
3. (b)(ii)Disconnect the voltmeter from points P and Q. Reconnect the voltmeter across the 560 Ω resistor between points Q and S. Close the switch. Record VQS, the voltmeter reading across Q and S. VQS = ..................................................... V [1] Open the switch.[1]
4. (c)The current I in the circuit is calculated using the equation: I = VQS / R where R = 560 Ω. Use your reading in (b)(ii) to calculate the current I. I = ..................................................... A [1][1]
5. (d)Calculate the resistance RLDR of the LDR under normal lighting conditions using the equation shown. RLDR = VPQ / I RLDR = ..................................................... Ω [1][1]
6. (e)Disconnect the voltmeter from points Q and S. Reconnect the voltmeter across the LDR between points P and Q. Place the piece of card on top of the LDR. Close the switch. Record a new value of VPQ for the LDR in the dark. VPQ = ..................................................... V [1] Open the switch.[1]
7. (f)Compare your reading for VPQ with the LDR under normal lighting conditions in (b)(i) with VPQ with the LDR covered by card in (e). Suggest what causes the change in the voltmeter readings as the intensity of the light reaching the LDR decreases.[1]
8. (g)Close the switch. Hold the card horizontally about 50 cm above the LDR. Slowly move the card towards the LDR until it rests on top of the LDR. Observe the reading on the voltmeter as you move the card. Open the switch. Describe the changes you see to the voltmeter reading as the card is moved downwards.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.