Current Electricity

A voltmeter is a high resistance device and is always connected in parallel with the circuit. While an ammeter is a low resistance device and is always connected in series with the circuit. So, to use voltmeter in place of ammeter a high resistance must be connected in series with the circuit.

In 1st case: Using the formula where is resistance of wire, V is voltage across wire and P is power dissipation in wire and From eqs. (1) and (2) ...(1) In 2nd case: Let is net resistance ...(2) Hence, from eqs. (3) and (4)