Question

A voltmeter must be connected in parallel with a circuit component to correctly measure the potential difference across the component. Which of the following explains why the voltmeter should have a very large resistance?

A. A large resistance is needed to make sure the voltmeter has the same current through it as the circuit component, so the potential difference across the voltmeter is the same as that across the component.
B. A large resistance is needed to make sure a large current passes through the voltmeter, so the rest of the circuit is not affected.
C. A large resistance is needed to make sure the current through the voltmeter has the same nonnegligible value whenever it is used, regardless of the current in the rest of the circuit.
D. A large resistance is needed to make sure negligible current passes through the voltmeter, so the rest of the circuit is not affected.

Answer 1

The voltmeter must have a very large resistance to ensure that it does not significantly alter the circuit's conditions, allowing for accurate voltage measurement without affecting the component's operation.

Step-by-step explanation:

A voltmeter measures the potential difference across a component in an electrical circuit by being connected in parallel to that component. It is crucial for the voltmeter to have a very large resistance, and there are important reasons for this. When the voltmeter's resistance is very high compared to the resistance of the component it is measuring, the current flowing through the voltmeter will be negligible. This results in minimal alteration to the overall current distribution in the circuit, thereby ensuring the measurement does not significantly affect the circuit's operation.

If the voltmeter had a resistance comparable to the circuit component, this would result in a significant change to the circuit's equivalent resistance when connected in parallel. Consequently, the measured voltage would not reflect the actual potential difference across the component as it would have been without the voltmeter connected. Therefore, to accurately measure the voltage without influencing the circuit itself, the voltmeter's resistance must be several orders of magnitude larger than that of the component it is measuring.