A Level Physics Practice Exam

In a potential divider circuit with a resistor and an LDR, what is the effect of increasing the intensity of light on the voltmeter reading across the resistor?

1. The voltmeter reading decreases

2. The voltmeter reading remains constant

3. The voltmeter reading increases

4. The voltmeter reading fluctuates

The correct answer is: The voltmeter reading increases

In a potential divider circuit that includes a resistor and a light-dependent resistor (LDR), the behavior of the circuit changes with variations in light intensity. As the light intensity increases, the resistance of the LDR decreases. This drop in resistance causes more current to flow through the circuit. In a potential divider, the voltage across the resistor is directly proportional to its resistance relative to the total resistance of the circuit. When the LDR's resistance decreases due to increased light intensity, the total resistance of the circuit changes. As a result, the voltage drop across the resistor increases, leading to a higher voltmeter reading. Therefore, as the intensity of light increases, the voltmeter reading across the resistor increases as well, which corresponds to the correct answer.