A student connects the circuit shown - Edexcel - A-Level Physics - Question 9 - 2023 - Paper 1

To find the voltmeter reading when the variable resistor is at a different value, we use the potential divider formula:

$V = R_2 \left( \frac{V_{source}}{R_1 + R_2} \right)$ where:

• $V_{source} = 6.0V$ (the battery voltage)
• $R_1 = 10Ω$ (fixed resistor)
• $R_2$ is the resistance of the variable resistor.

As $R_2$ varies from 0Ω to 40Ω, we can calculate the voltmeter reading at $R_2 = 40Ω$:

$V = 10Ω \left( \frac{6.0V}{10Ω + 40Ω} \right) = 10Ω \left( \frac{6.0V}{50Ω} \right) = 1.2V$

Thus, the minimum reading on the voltmeter is 1.2 V.

When the variable resistor is set to 40Ω, the voltmeter will read:

$V = 1.2V$

So the minimum reading on the voltmeter is 1.2 V.