# What Is Voltage?

## What is Voltage?

In practical terms, voltage is the difference in electrical potential between two points in a circuit. The unit of measurement is the volt (V), which is a measure of the energy per unit charge.

Voltage is one of the properties of an electric field and can be measured in terms of:

• its relationship to a common point. This is usually with respect to ground (zero volts)
• the relationship between two points. This is usually known as the voltage across a device or the voltage across a circuit.

In physical terms, Voltage is the work required to move an electric charge between two points:

1 Volt is the force required to send one ampere of current through a resistance of one Ohm.

## Some Formulae

• $V = \sqrt{PR}$
• $V = I \times R$
• $P = V \times R$

where V = potential difference (volts), I = current intensity (amps), R = resistance (ohms), P = power (watts).

## Voltage across Resistors, Capacitors and Inductors

Voltage cross a resistor (Resistor R):

• $V_R = IR_R \!\$

Voltage across a capacitor (Capacitor C):

• $V_C = IX_C \!\$

Voltage across an inductor (Inductor L):

• $V_L = IX_L \!\$

Where V=voltage, I=current, R=resistance, X=reactance.