Electrical Instruments

A galvanometer acting as a voltmeter will have a high resistance in series with its coil.

A galvanometer requires a very small current to cause notable deflection in the dial. Thus, it is a very sensitive instrument. A galvanometer can be converted to a voltmeter by making the resistance higher. This can be done by adding it in parallel between the points across which we intend to measure the voltage drop. This makes the galvanometer exposed to the same voltage value that is being measured.

A voltmeter is thus a modified form of a pivoted coil galvanometer. To prevent damage to the instrument, only a small current needs to be passed through it which is achieved by putting a high resistance in series with the galvanometer coil. The resistance value is dependent on the working range of the voltmeter.
Also Read: Current Electricity