This question examines the use of voltmeters in an electrical circuit by considering the effect they might have on the circuit itself.Consider again an electrical circuit containing an emf source and several resistors. Some resistors might be in series with other resistors, and some resistors might be in parallel with other resistors.If we want to measure the potential difference across one particular resistor—let's say of resistance, R —we will need to place a voltmeter in the circuit. Suppose that the voltmeter has a resistance, RV . In order for the voltmeter to measure the potential difference across the resistor, it must be placed in parallel with the resistor.
(a) What will the overall resistance of the voltmeter and resistor now be?
(b) So, will the placing of the voltmeter have changed the circuit? That is, will the placing of the voltmeter have changed the potential difference (which we wanted to measure) across the resistor? Explain your answer.
(c) So, ideally, what should the resistance of a voltmeter be?