# What is Voltage â€“ Definition, Formula, Unit, Types and Methods of Measurement

## What is Voltage?

Voltage, also called potential difference, electric pressure or electric tension, is defined as the difference of electric potentials of two points in an electric circuit. In other words, the amount of energy required to move an electric charge from one point to another in an electric circuit is called voltage.

Voltage is denoted by the symbol V or v, where V is used to represent a constant voltage, while v is used to represent a time-varying voltage. In this article, we will learn all about voltage, and the methods used for measuring the voltage in an electric circuit.

Mathematically, voltage is defined as the ratio of the work done to the electric charge, i.e.,

$$\mathrm{Voltage, V=\frac{Work\: done\, (W)}{Charge \,(Q)}}$$

Where, the work done is measured in Joules (J) and charge in Coulombs (C). Therefore, the unit of voltage is Joules per Coulomb (J/C).

The voltage in an electric circuit forces the electric charges (or electrons) to flow through the circuit. Therefore, the voltage is entirely responsible for the flow of electric current through an electric circuit. If there is no voltage, no current flow.

In order to understand the voltage between two points in an electric circuit, consider the two points say A and B. Thus, by the definition of voltage, the electric potential of point A with respect to the point B is defined as the amount of work done required to move a unit charge from point A to point B under the influence of an electric field (E).

Mathematically, the voltage between points A and B can be expressed as,

$$\mathrm{V_{AB}=V_{A}-V_{B}}$$

## Unit of Voltage

The SI unit of voltage is Volt (V). It is named in honor of an Italian physicist Alessandro Antonio Volta (1745-1827), who invented first electric battery, the voltaic pile. However, the base unit of voltage is Joules per Coulomb.

## Formulae of Voltage

According to Ohmâ€™s law, the voltage is given by the product of resistance of the conductor and current flowing through it, i.e.,

$$\mathrm{Voltage,V=I\times R}$$

Voltage may also be expressed in terms of power and current in the circuit as,

$$\mathrm{\because P=VI}$$

$$\mathrm{\therefore Voltage,V =\frac{P}{I}}$$

We may express the voltage in a circuit in terms of power and resistance as well.

$$\mathrm{\because P =\frac{V^{2}}{R}}$$

$$\mathrm{\therefore Voltage,V =\sqrt{P\times R}}$$

## Types of Voltage

Depending on the variation in polarity of the voltage with respect to time, it is classified into in two basic types, namely,

• Direct Voltage
• Alternating Voltage

When the polarity of voltage in an electric circuit does not change with time, it called direct voltage. It named so because it acts in only one direction. The direct voltage may be a constant voltage or a pulsating voltage. In case of constant voltage, the magnitude of voltage does not change with time, while in case of the pulsating voltage, the magnitude changes with respect to time.

On the other hand, when magnitude of the voltage changes continuously and direction changes periodically, then the voltage is known as alternating voltage. The alternating voltage can have different types of waveforms like sinusoidal waveform, square waveform, triangular waveform and many more. In actual practice, the alternating voltage mostly has sinusoidal waveform due to several technical and economic reasons.

## Sources of Voltage

The energy sources that we use in electrical circuits and systems are voltage sources. The most common sources of voltage are cell, battery, dc generator, alternator, etc. In electric circuits, the voltage sources are represented by the symbols shown in Figure2.

## Measurement of Voltage

The measurement of electric voltage in an electrical or electronic circuit is one of the essential measurements. The voltage in any electrical or electronic circuit is always measured between two points. The measuring instrument used for voltage measurement is called voltmeter.

In a three-phase electric circuit, we can measure two voltages namely, phase voltage and line voltage. The phase voltage is measured between any one phase and neutral wire. Whereas, the line voltage is measured between any two phases. Now, let us discuss the most common methods used to measure the voltage in electric circuits.

## Voltmeter Method

In this method of voltage measurement, a voltmeter of suitable range is used to measure the voltage between any two points in the circuit. In this method, the voltmeter is connected in parallel with the circuit component whose voltage is to be measured as shown in Figure3.

The voltmeter connected across the two points measures the voltage drop between them when current flow through the circuit.

## Digital Multimeter Method

These days, digital multimeters are very popular among electrical engineers and professionals because of their simplicity and versatility. We can use a digital multimeter to measure the voltage between two points in an electric circuit.

In this method, the two leads (called probes) of the digital multimeter are connected to the two points across which the voltage to be measured as shown in Figure4. The digital multimeter measures and displays the voltage readings on an LCD screen in the form of digits. The major advantage of this method is that we can measure both direct voltage and alternating voltage with the same device just by changing the meter settings.

## Summary

• Voltage is the work done required to move a unit charge from one point to another point in an electric circuit.

• Voltage is also called as electric pressure, potential difference, or electric tension.

• The SI unit of voltage is volt (V).

• Voltage is the essential parameter in the circuit for the flow of current. If there is no voltage, no current flow.

• Voltage is broadly classified into two basics types: direct voltage and alternating voltage.

• In an electrical or electronic circuit, we can measure the voltage by using either a voltmeter or a multimeter.