Before we start, you should have an understanding of the terms Power and Watts to do this activity. If you don’t (or you’d like a recap) then head over to the activity called ‘Understanding Power’.

Have you ever thought about how people work out how much you need to pay for electricity? You didn’t even know you have to pay off electricity, did you… Electricity costs money because it is a form of **power** and people have to spend money burning fuel to make the electricity. The more power you use the more you have to pay for that electricity. But how do you work out how much power one house is using? Luckily there are some equations we can look at to work out power, and that is what we are going to be doing in this activity.

First of all, there is a **power equation** that uses **current **and **voltage**. This should hopefully make sense as current is a measurement of how many electrons are flowing through the wire and voltage is a measurement of how much energy each one is carrying.

INSERT IMAGE OF EQUATION HERE

**P** = power (Watts (W))

**I **= current (Amps(A))

**V** = potential difference (Volts (V))

This second equation is a little tougher – but it comes from putting the first equation and V=IR together. It looks like this:

INSERT IMAGE IF EQUATION HERE

**P** = power (Watts (W))

**I **= current (Amps (A))

**R** = resistance (Olms (Ω))

Let’s take a look at an example.

Q –

A kettle uses 400 V with a current of 3 A. Calculate the power of the kettle.

**Step 1** – highlight all of the number in the equation:

A kettle uses 400 V with a current of 3 A. Calculate the power of the kettle.

**Step 2** – Write out the numbers next to their symbols:

P = ?

I = 3 A

V = 400 V

**Step 3 **– put the numbers into the equation:

P = 3 x 400

**Step 4 **– do the maths and write your answer:

P = 1,200 W

Don’t forget your units!

Let’s try some questions on that!