A galvanometer coil has a resistance of `12Omega` and the meter shows full scale deflection for a current of `3mA`. How will you convert the meter into a voltmeter of range 0 to 18V?

Explanation

Resistance of the galvanometer coil, `G = 12 Omega`
Current for which there is full scale deflection, `I_(s) = 3mA = 3 xx 10^(-3)A`
Range of the voltmeter is 0, which needs to be converted to 18V.
`:. V = 18V`.
Let a resistor of resistance R be connected in series with the galvanometer to convert it into a voltmeter. This resistance is given as:
`R = (V)/(I_(s)) -G`
`=(18)/(3 xx 10^(-3)) - 12 = 6000 - 12 = 5988 Omega`
Hence, a resistor of resistance `5988Omega` is to be connected in series with the galvanometer.