Question

Which of the following is likely to have the largest resistance?

• A. Voltmeter of range 10 V
• B. Moving coil galvanometer
• C. Ammeter of range 1 A
• D. A copper wire of length 1 m and diameter 3 mm

Answer 1

The correct option is A Voltmeter of range 10 V

Voltmeter of range 10 V is likely to have the largest resistance.

Voltmeters by definition measure potential difference so it must be connected in parallel to measure the voltage change across something (a resistor).

Since voltmeters must be in parallel, as parallel branches have equal voltages, the connection of the voltmeter must not interfere with the behavior of the circuit (for example, disrupting the current “allocated” to a resistor). Therefore, to prevent any current from going into the branch with the voltmeter, it's resistance is made extremely high, so that very little current goes through the voltmeter branch.

($V=IR$ and $V_{voltmeter}=V_{resistor}$ so when R is high for the voltmeter, I must be very small in value)