charge Coulomb (C)

current Ampere (A)

energy  Joule (J)

potential difference  Volt (V)

power  Watt (W)

resistance  Ohm (Ω)

time  second (s)

Current, Potential Difference & Resistance

Circuit symbols are used to make sure everyone understands the diagram clearly and to avoid mistakes being made.

The symbols you need to be able to draw and name are:

Circuit Symbols
Circuit Symbols

For electrical charge to flow through a closed circuit the circuit must include a source of potential difference, measured in Volts. Charge is measured in Coulombs.

Electric current is a flow of electrical charge. Current is measured in Amps.

The size of the electric current is the rate of flow of electrical charge.

Learn THIS DEFINition

Charge flow, current and time are linked by the equation:

charge flow = current × time

charge flow = current × time

charge flow = 40 x 1800

The charge flow is 72000 Coulombs

charge flow = current × time

charge flow = 0.5 x 17

The charge flow is 8.5 Coulombs

A current has the same value at any point in a single closed loop.

Resistance is measured Ohms.

The Potential Difference is the energy transferred to/from each unit of Charge.

Unit: Volt (1 Volt = 1 Joule/Coulomb)

Learn this definition

The current (I) through a component depends on both the resistance (R) of the component and the potential difference (V) across the component.

The greater the resistance of the component the smaller the current for a given potential difference (pd) across the component.

Current, potential difference or resistance can be calculated using the equation:

potential difference = current × resistance

potential difference = current × resistance

potential difference = 0.8 x 2.5

The potential difference is 2 Volts

potential difference = current × resistance

3.3 = 0.15 x resistance

resistance = 3.3 / 0.15

The resistance is 22 Ohms