Meet the characters

How much is vital

Doing the best or right thing depends on right thinking. So on paying attention to how much, and not just describing with words. Fortunately you can use pictures of how much to help your thinking.

How much - power

How much power is measured in watts or kilowatts (thousands of watts). This number is often written on the outside of an appliance, where you might find watts abbreviated to W and kilowatts abbreviated to kW.

How long - hours, minutes or seconds

How long an appliance is on for might be measure in hours, minutes or seconds. You decide this with a switch. An automatic switch might do it for you at home:

Some devices, such as overnight heaters might be controlled by two switches for time and for temperature.

How much you 'use'- the cost box

How much you'll get charged is set by the power and how long. A high power device might cost as much in a day as a low power device that's left on for longer.

The height of the box shows the power. The width of the box shows how long. The are shows what you'll have to pay for – the kilowatt-hours. kilowatt-hours = kilowatts × hours

Describing a pattern of use

With these three:

durations – how long: the hours power – how much you're demanding: the kilowatts cost boxes - a combination of how long and how much you're demanding: the kilowatt-hours

You can build a description of a day's use of electrical devices. You're paying for the units you demand over the day: the energy.

Collaborating quantities

Physical quantities and how they interact are at the basis of an understanding.

Power arrow Cost box How long clock? Pie? Energy bar