E3: Electrical energy — C level

Power is measured in Watts. It is how fast energy is being used.

You can work out how much power an appliance uses with this formula:

P = VI

P: Power (in W – Watts).

V: Voltage (in V – Volts).

I: Current (in A – Amps).

Section 1

The power formula is:

P = VI

Use it to work out the power in the lamps in series and parallel circuits that you made in the simulator activity.

1. Series: 4.5V, 0.45A.
2. Parallel: 9V, 0.9A.

Use the answers above to explain why the lamps in parallel were brighter.

Section 2

We can rearrange the power formula to work out the current. The formula looks like this:

I = P÷V

Electricians need to know the current so that they can make the wires big enough to not melt.

Work out the current used by each of the appliances above. The voltage to use is the mains voltage, V=240V.

1. Air conditioner cooling (2500W)
2. Air conditioner heating (3200W)
3. Bar heater (1000W)
4. LED light bulb (11W)
5. Stove hotplate 1 (1000W)
6. Stove hotplate 2 (1400W)

Section 3

Electrical appliances usually have voltage and current written on them.

The voltage is the design voltage - the appliance won’t work correctly with different voltages.

The current is the maximum current - the appliance doesn’t always use this amount of current. Sometimes it’s not working as hard, just like a car engine works harder when it’s making you speed up than when it’s cruising at a constant speed.

Write:

Use the example of an air conditioner to explain this concept.