Using A Voltmeter to Measure Potential Difference

The potential difference across a load in a circuit is measured by an instrument called the voltmeter. The voltmeterr has a needle moving over a graduated scale. It gives the value of potential difference across the terminals. Voltmeter has two terminals marked +ve and -ve. The terminal marked +ve is connected to the higher potential side of the circuit with a wire, while the -ve terminal is connected to lower potential side of the circuit.

To measure the potential difference across two end points in a circuit, a voltmeter is connected in such a way that the potential difference across the component is same as that across the voltmeter. Such a connection is called a parallel connection. In Figure below the potential difference across the load is same as across the voltmeter. The reading of the voltmeter gives the potential difference across the load. Note that if the voltmeter is removed, there will be no gap in the circuit, and the current through the circuit will  not stop.

Two or more electric elements are said to be connected in parallel if the potential difference across one is the same as he potential difference across the other. A voltmeter is always connected in parallel in a circuit.

As the Voltmeter is to be connected in parallel so the voltmeter has very high resistance. Hence a very less amount of current flows through the voltmeter and the change in the current that is flowing through the load is negligible.