# What is Electricity?

Electricity is electrons – the negative charge which orbits around the nucleus of an atom.

## Coulomb

The Coulomb is the measure of the quantity of electrons. Just as litres or gallons is used to measure the quantity of a liquid, Coulombs is used to measure the quantity of electrons.

A Coulomb contains approximately 6.24 × 1018 electrons.

A Coulomb is defined as:

“The quantity of electric charge transported in 1 second by a current of 1 ampere.” – The International System of Units

C = A⋅s

The symbol for the Coulomb is the upper case letter C.

It is derived from the basic SI units of ampere and second.

## Ampere

The ampere (often shortened to amp) is the measure of the flow of electrons. Just as litres per second or gallons per second is used to measure the flow of a liquid, Amperes is used to measure the flow of electrons.

It is equal to the constant flow of one Coulomb of charge over one second.

A = C / s

The official SI definition is:

“The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per metre of length.” – The International System of Units

The symbol for the Ampere is the upper case letter A.

This is a fundamental or basic SI unit.

## Volt

The volt is the measure of the electromotive force (e.m.f), electrical pressure, or “push” that moves electrons from one place to another. Just as Pascals or pounds per square inch are used to measure the pressure exerted by a liquid, Volt is used to measure the electrical pressure.

The Volt is defined as:

“The volt is the potential difference between two points of a conducting wire carrying a constant current of 1 ampere, when the power dissipated between these points is equal to 1 watt.” – The International System of Units

V = W / A

The volt used to be defined as:

The force required to for one ampere of current to flow through a resistance of one ohm.

V = A⋅Ω

The symbol for the Volt is the upper case letter V.

It is derived from the basic SI units of Ampere and the derived SI unit of Watt.

## Ohm

The Ohm is the measure of a material’s resistance to the flow of electrons.

The Ohm is defined as

“The resistance through which a current of one ampere flows when an electromotive force of one volt is applied across it.” – The International System of Units

Ω = V / A

The symbol for the Ohm is the upper case Greek letter Omega: Ω.

The ohm used to be defined as:

The resistance of a column of mercury 106.3cm long with a cross sectional area of 1 square millimetre (or 41.85 inches long with a cross sectional area of 0.0015 square inches).

It is derived from the basic SI unit Ampere and the derived SI unit Volt.

## Watt

The Watt is the measure of power.

The electrical Watt is defined as

The power which does one Joule of work in one second.

W = V⋅A

The symbol for the Watt is the upper case letter W.

It is derived from the basic SI unit second and the derived SI unit of Joule.

## Difference Between Amperes and Volts

Amperes is the rate at which electricity is flowing in the circuit, while volts is the pressure that causes the electricity to flow.

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