Voltmeter
A voltmeter is used to measure electric potential, also known as electromotive force. The measurements taken by a voltmeter use units of volts, and it is common to say that a voltmeter is used for measuring voltages. A voltmeter is attached in parallel across the portion of the circuit where potential is to be measured.
In an electric circuit, electric potentials, are the differences in voltages between one point in the circuit and another. For example, in the circuit shown below, Vab is the voltage measured between point a and point b across the resistor.
To measure the voltage between points a and b, the voltmeter is attached across points a and b in parallel as shown in the next figure.
