Electrical current depends on resistance and potential difference. Different electrical components have different characteristics. These can be investigated using suitable circuits and apparatus.

Power is the rate of transfer of energy between energy stores.

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

The energy transferred can be calculated using the equation:

energy transferred = power × time

This is when:

- energy is measured in joules (J)
- power is measured in watts (W)
- time is measured in seconds (s)

A 50 W lamp is switched on for 60 s. Calculate the energy transferred.

energy transferred = power × time

= 50 × 60

= 3,000 J (or 3 kJ)

The energy transferred can be calculated using the same equation but with different units:

- energy is measured in kilowatt-hours (kWh)
- power is measured in kilowatts (kW)
- time is measured in hours (h)

A 500 W television set is switched on for 4 hours. Calculate the energy transferred.

500 W = 500/1000 = 0.5 kW

energy transferred = power × time

= 0.5 × 4

= 2 kWh

Electrical power can be calculated using the equation:

power = potential difference × current

This is when:

- power is measured in watts (W)
- potential difference is measured in volts (V)
- current is measured in amps (A)

A current flows through a 2.0 A electric drill at a potential difference of 230 V. Calculate the power dissipated.

power = potential difference × current

= 230 × 2.0

= 460 W

Electrical power can also be calculated using the equation:

power = (current)^{2} × resistance

This is when:

- power is measured in watts (W)
- current is measured in amps (A)
- resistance is measured in ohms ( )

A current of 3 A flows through a 10 resistor. Calculate the power dissipated.

power = (current)^{2} × resistance

= 3^{2} × 10

= 9 × 10

= 90 W