Power, potential difference and current

Heating up wires

The amount of energy transferred each second (power) between the energy stores can be calculated using the equation:

power = potential difference × current

\text P = \text V \times \text I

This is when:

One watt is equal to one joule per second (J/s).

Power can also be written as:

power = (current)2 × resistance

\text{P} = \text{I}^{2} \times \text{R}

This is when:

  • power ( \text{P}) is measured in watts (W)
  • current ( \text{I}) is measured in amperes, often referred to as amps (A)
  • resistance ( \text{R}) is measured in ohms (Ω)


How much energy is transferred each second by a current of 2 amps (A) driven by a potential difference of 230 volts (V)?

\text P = \text I \times \text V

= 2 × 230

\text{P} = 460 W


What power is dissipated by a current of 3 A through a 10 Ω resistor?

\text{P} = \text{I}^{2} \times \text{R}

= 32 × 10

= 9 × 10

\text{P} = 90 W