Power!Power is a measure of how quickly energy is transferred. The unit of power is the watt, W.

The more energy that is transferred in a certain time, the greater the power.

A 100 W light bulb transfers more electrical energy each second than a 60 W light bulb.

Power!Power is a calculated by using this equation:

For example, what is the power of a 5 A, 1.5 V lamp?

P = I × V

Power = 5 × 1.5 = 7.5 W

Energy from the energy source

Thermal energy

Light

Energy efficient light bulb

Where the Energy at?

Energy from the energy source

Light

Thermal energy

Energy inefficient light bulb

Where the Energy at?

What fuse to use?Fuses restrict current.

Fuses come in standard ratings of 3 A, 5 A or 13 A.

Multi-boxes have fuses to restrict the current that flows into them – otherwise, they will overheat and blow up!

P = I × V

What fuse to use?Fuses blow if the current they restrict is exceeded – avoiding the multi-box from blowing up!

Which fuse should be used for a multi-box with a 1,150 W heater and a 50 W lamp plugged into it? The multi-box is plugged into the mains (240 V). The circuit is parallel.

P = I × V

What fuse to use?Which fuse should be used for a multi-box with a 1,150 W heater and a 50 W lamp plugged into it? The multi-box is plugged into the mains (240 V).

I =

I =

= 5.0 A - Therefore use the 13A fuse.