Energy Transfers in Electrical Appliances and the National Grid — AQA GCSE Physics
Electrical appliances transfer energy from the mains, and the National Grid distributes electricity efficiently.
Energy transfers in appliances
Everyday appliances are designed to bring about energy transfers. When charge flows, work is done and energy is transferred from the mains supply to the appliance and then to useful (and wasted) stores. For example:
- a kettle: electrical → thermal store of the water,
- a motor: electrical → kinetic store,
- a lamp: electrical → light (and some heat).
The amount of energy transferred depends on the power of the appliance and how long it is switched on: $$E = P \times t$$
The National Grid
The National Grid is a system of cables and transformers that carries electricity from power stations to consumers (homes and industry).
- Step-up transformers increase the potential difference for transmission.
- Step-down transformers decrease it again for safe use.
Why high voltage is used
Transmitting at high voltage means a lower current is needed for the same power. A lower current means less energy is wasted as heat in the cables (because power loss depends on current²), making transmission efficient.
Exam tips
- Appliances transfer energy from the mains; amount depends on power and time (E = Pt).
- The National Grid uses step-up then step-down transformers.
- High voltage → low current → less energy wasted as heat in cables.
- This makes long-distance transmission efficient.