## Some Definitions

## Current

A current is a flow of charged particles. It is how fast the electrons are flowing through a circuit. The official definition is '

When electricity was first observed scientists did not know about electrons: they decided that current was the flow of positive charges which were repelled by the positive electrode and attracted to the negative electrode. We call this

*charge per unit time'*or '*the rate of flow of charged particles'*. The current will be higher if the voltage is higher and lower if there is a high resistance. It is measured in Amps (A).When electricity was first observed scientists did not know about electrons: they decided that current was the flow of positive charges which were repelled by the positive electrode and attracted to the negative electrode. We call this

**conventional current.**We now know that electricity is the flow of negative electrons and that the current flows the in the opposite direction around a circuit.## Charge

Charge is a property of a material. It can be positive, negative or neutral. It is measured in Coulombs (C). It is related to current (A) and time (s) in the following equation:

## Voltage

Voltage is officially defined as

It is related to charge and energy in the equations below.

*'energy per unit charge'*. It can be thought of either as how much energy each electron is given as it passes through the battery or power supply. Or you can think of it as how hard the electrons are being pushed around the circuit. It is measured in Volts (V). Voltage is also called**potential difference**as it is the difference in Volts between the two electrodes.It is related to charge and energy in the equations below.

*Energy (J)= Voltage (V) x Charge (C)*

Energy (J) = Voltage (V) x Current (A) x Time (s)

Power (W) = Voltage (V) x Current (A)

Energy (J) = Voltage (V) x Current (A) x Time (s)

Power (W) = Voltage (V) x Current (A)