Explanation

(a) A voltmeter is an instrument used to measure the potential difference between two points in an electrical circuit directly in volts. Voltmeter is essentially a galvanometer which is connected in parallel across two points in the circuit between which the potential difference is to be measured. The potential difference read by the voltmeter is slightly less than the actual value to be measured. Hence, the resistance of the voltmeter should be as high as possible so, that on connecting it in a circuit across two points the potential difference may not fall appreciably.
Hence, a voltmeter is made by connecting a high resistance in series with a pivoted type moving coil galvanometer G. The value of R depends upon the range of the required voltmeter.