Draw a diagram of the circuit arrangement, using the correct symbols for the components in the circuit. Select from the symbols shown in Fig. 1.1.
On your circuit in (a), draw a voltmeter connected across the LDR to measure the potential difference (p.d.) across the LDR. Use the circuit symbol for a voltmeter.
The voltmeter reading $V_1$ is shown in Fig. 1.2. Record the voltmeter reading $V_1$.
Suggest why the switch is opened after the voltmeter reading has been recorded.
The student removes the voltmeter, reconnects it across the 560 Ω resistor, closes the switch, notes the voltmeter reading $V_2$ and then opens the switch. The measured value of $V_2$ is 2.18 V. The current $I$ in the circuit is found from $I=\frac{V_2}{R}$ where $R=560\,\Omega$. Calculate the current $I$.
Use your answers from (b)(ii) and (c)(i) to calculate the resistance $R_{\mathrm{LDR}}$ of the LDR under normal lighting conditions, using the equation $R_{\mathrm{LDR}}=\frac{V_1}{I}$.
The student disconnects the voltmeter from across the 560 Ω resistor, reconnects it across the LDR, puts a piece of card above the LDR so that light cannot reach the LDR, closes the switch, records the voltmeter reading $V_3$ and then opens the switch. The measured value of $V_3$ is 1.94 V. Compare $V_1$, measured under normal lighting conditions in (b)(ii), with $V_3$, measured in the dark. Suggest what causes the change in the readings as the intensity of the light reaching the LDR decreases.
The student keeps the card horizontally 50 cm above the LDR, slowly lowers the card towards the LDR until it rests on top of the LDR, and watches the voltmeter readings across the LDR as the card is moved. Table 1.1 gives the voltmeter readings as the distance $d$ between the card and the LDR decreases. Describe the relationship between $d$ and $V$ shown by these readings.