To keep the effect of a voltmeter on a circuit to a minimum, the internal resistance of the voltmeter must have which of the following relationships to the circuit load?
A. Equal to
B. Lower than
C. Higher than
D. In proportion to
Share your understanding of this question with the correct explanation.
The correct answer is C. Higher than.
In an electrical circuit, a voltmeter is used to measure the voltage difference between two points. To avoid significantly altering the circuit and introducing measurement error, the voltmeter should have a very high internal resistance compared to the circuit load. This ensures that the voltmeter draws negligible current from the circuit it’s measuring, keeping the effect of the voltmeter on the circuit to a minimum.
By having an internal resistance much higher than the circuit load, the voltmeter effectively becomes an ‘open circuit’ for the path it’s connected across, thus, it does not disturb the original circuit conditions. Therefore, the voltmeter gives an accurate reading of the voltage, as if it was not there. This is why real-world voltmeters are designed to have an internal resistance in the megaohms range.