What is Voltage?

Potential difference or voltage, Explained.


Voltage is the driving force of current, it is the electromotive force which pushes free electrons from one atom to another in the same direction. Confused by this? if so then click here to first learn how electricity works.

How to imagine Voltage

It is easiest to think of voltage like pressure in a pipe. When there is a higher voltage (pressure) then a stronger current will flow. Although it is important to understand that voltage (pressure) can exist without a current (flow), but current cannot exist without voltage (pressure).

Water analogy

Voltage is often referred to as potential difference, this is because there will be a difference in the potential energy of the electrons, between any two points in a circuit. As electrons flow through a battery, their potential energy is increased but as they flow through a light bulb, their potential energy will decrease, this energy will leave the circuit as light and heat.

Take a regular 1.5V AA Battery for example, between it’s two terminals (+ and -) there’s a potential difference of 1.5 Volts.

1.5V AA Battery

Voltage, or potential difference, is simply a measurement of the amount of energy (Joules) per unit of charge (Coulomb). E.g. in a 1.5V AA battery, every coulomb (charge) will receive 1.5 volts, or Joules of energy.

Voltage = Joules ÷ Coulomb

1 Volt = 1 Joule per coulomb

100 Volts = 100 Joules per coulomb

1 coulomb = 6,200,000,000,000,000,000 electrons (6.2×1018)

Measuring Voltage

We measure voltage in the unit of “Volts” which will usually be represented simply by the letter “V” on drawings and technical literature. It is often necessary to quantify an amount of voltage, this is done so according to SI units, the most common quantities of voltage you will see are:

  • megavolts (MV)
  • kilovolts (kV)
  • volts (V)
  • millivolts (mV)
  • microvolts (μV)

Voltage is always measured across two points with a device called a Voltmeter. Voltmeters are either analog of digital, the latter being the most accurate. Voltmeters are usually built into portable digital multimeter devices, as illustrated below, they are a common and often essential tool for any electrician or electrical engineer. You will usually find analog voltmeters on older electrical panels such as switchboards and generators, but almost all new equipment will come with digital meters as standard.


Portable digital multimeter with a voltmeter function

Voltmeter Analog
Analog Voltmeter

On electrical schematics, you will see voltmeter devices denoted by the letter V within a circle, as illustrated below:

Voltmeter symbol
Voltmeter symbol


Calculating Voltage

In electrical circuits, the voltage can be calculated according to Ohm’s triangle. To find voltage (V) simply multiply current (I) by resistance (R).

Voltage = Current / Resistance


Current in circuit  = 10Amps
Resistance of circuit =

Voltage = 10A x

Answer: 26V



Ohm's VIR triangle


  • Voltage is the force which moves electrons from one atom to another
  • Voltage is also known as potential difference
  • Voltage is measured by the unit “volts” (V)
  • Batteries increase potential energy of electrons
  • Light bulbs, and other loads, decrease electron potential energy
  • Voltage is measured with a voltmeter
  • The Voltage of a circuit can be calculated by multiplying the current and resistance

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