Can I download and print the Mains Electricity & the National Grid cheat sheet?

Yes. It is free to download as a PNG or PDF using the buttons above, and you can print it for your own revision. Teachers are welcome to print it as a classroom poster or handout.

Does it work for my exam board?

Yes. It sticks to the ground shared by AQA, Edexcel, OCR and WJEC, so it works whichever board you are sitting, at Foundation or Higher tier, for combined science and triple science alike.

How should I use this physics cheat sheet for revision?

Work through the poster one section at a time, starting with a.c. vs d.c.. Cover each section and check what you can remember, then use the written version below to fill in any gaps. When you want more depth, Cognito has videos, quizzes and exam questions on the same topic.

Mains Electricity & the National Grid – GCSE Physics Cheat Sheet

on this cheat sheet

Everything on the GCSE Physics Mains Electricity & the National Grid poster is written out below, section by section. Use it to search the sheet, copy parts into your own notes, or check a fact quickly.

A.C. vs D.C.

Alternating current (A.C.) constantly changes direction. UK mains supply is A.C. at approximately 230 V and a frequency of 50 Hz. Direct current (D.C.) flows in one direction only and is produced by a direct potential difference, such as a cell or battery.

Three-core cable

A mains plug and cable contains three wires, each with a specific role.

Earth (green and yellow) - is at 0 V. It only carries current if there is a fault, to stop the casing becoming live.
Live (brown) - carries the alternating potential difference from the supply (~230 V).
Neutral (blue) - completes the circuit and is at about 0 V.

Mains safety

Your body is at 0 V, so touching the live wire creates a large potential difference across you, driving a current through your body.
A live wire is dangerous even when the switch is open, because there is still a potential difference on it.
Fuses melt and break the circuit if too much current flows. This means we need a fuse with a rating higher than the current flowing through it.

Example: An electric kettle is rated at 1,150 W and is connected to a 230 V mains supply. What fuse should it use?

I = P ÷ V = 1,150 ÷ 230 = 5 A

Choose a 5 A fuse (must be higher than 5 A, so a 13 A fuse is selected).

The National Grid

Electricity travels from power station → step-up transformer → high-voltage transmission cables → step-down transformer → homes and industry.

Electricity needs to be transmitted at a low current to reduce energy losses in the cables.
To transmit the same power at a lower current, the voltage must be increased.
Step-up transformers increase the voltage for transmission (to 400,000 V).
Step-down transformers reduce it again before it reaches homes and businesses.

For an ideal transformer:

Vp ÷ Vs = Np ÷ Ns

Where Vp and Vs are the primary and secondary voltages, and Np and Ns are the number of turns on the primary and secondary coils.