Conversion of Moving Galvanometer into Voltmeter

A voltmeter is nothing but a high resistance galvanometer. A voltmeter is constructed by connecting a high resistance R in series with a pivoted type moving-coil galvanometer G. This makes the effective resistance of the galvanometer very high.

Let us convert a galvanometer of resistance G into a voltmeter of a range V volt. Let us suppose that a current Ig passing through it is able to cause full scale deflection. The value of the resistance R to be placed in series with the coil is then given by
            Ig = V/R + G
Or            R = V/ig – G

Thus when a resistance of this value is connected in series with the galvanometer works as a voltmeter of range 0-V volt.