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# Comparing Power

### Comparing Power

We will use real world appliances to compare how the value of power can differ depending on its factors.

**True** or **false**? Energy transferred and work done are all we need to calculate power.

Other than energy transferred or work done, what else do we need to calculate the power of a system?

Which of these is the correct formula for calculating power? Select all the options you think are correct.

You can select multiple answers

If two machines use the same amount of energy to lift the same weight to the same height, but machine A does it quicker than machine B, then which machine has more power?

Two electric motors are used to lift a 5N weight through a vertical height of 20 m. Motor 1 does this in 5 seconds. Motor 2 does this in 10 seconds. Which motor has more power?

Remember that power is the **rate** **of** **energy** **transfer** (or work done). Therefore, if two machines lift the same weight to the same height, the machine which does it quicker will have more power.

**Complete the sentence:** If two toasters have the same energy, the toaster which toasts the bread slower has ________ power.

Because $P=\frac{E}{t}$, the longer the time taken, the smaller the power rating and vice versa.

What is meant by the **power** **rating** on electrical appliances?

Power rating of 40W means that 40 Joules of energy are transferred in 1 second. What device would you rather have in your kitchen? One with power rating 240W or one with power rating 40W?

The power rating on devices tells you how much power the device has.

Usually a **higher** **power** **rating** is preferred as it can ensure energy is transferred quicker. However, you also have to take into account how safe the device is, not just how much energy it can handle.