Direct and alternating current, plug wiring and safety, the power and energy equations, and why the National Grid uses transformers.
You can study this deck without signing up — your progress is kept in this browser. An account saves it properly, syncs it across devices, and lets you edit the cards.
1.What is direct current?
Current that flows in one direction only, produced by a source of direct potential difference such as a cell.
2.What is alternating current?
Current that repeatedly changes direction, produced by an alternating potential difference.
3.What type of supply is UK mains electricity?
Alternating current.
4.What is the frequency of UK mains electricity?
50 hertz.
5.What is the potential difference of UK mains electricity?
About 230 volts.
6.Name the three wires in a three core cable.
Live, neutral and earth.
7.What colour is the live wire?
Brown.
8.What colour is the neutral wire?
Blue.
9.What colour is the earth wire?
Green and yellow stripes.
10.What does the live wire do?
It carries the alternating potential difference from the supply.
11.What does the neutral wire do?
It completes the circuit and is at or close to earth potential, about 0 V.
12.What does the earth wire do?
It is a safety wire that carries current away only if there is a fault, keeping the case of an appliance at 0 V.
13.Why is the live wire dangerous even when a switch is off?
It is still at 230 V relative to earth, so touching it would cause a large current to flow through you to earth.
14.Why is touching a live wire dangerous?
Your body provides a path to earth, and the resulting current can cause severe injury or death.
15.Why is a fuse or circuit breaker used?
To break the circuit if the current becomes too large, preventing overheating and fire.
16.State the equation for power in terms of potential difference and current.
power = potential difference x current
17.State the equation for power in terms of current and resistance.
power = current squared x resistance
18.A device draws 3 A at 230 V. Calculate its power.
230 x 3 = 690 W.
19.State the equation for energy transferred in terms of power and time.
energy transferred = power x time
20.State the equation for energy transferred in terms of charge.
energy transferred = charge flow x potential difference
21.A 2 kW heater runs for 1800 s. Calculate the energy transferred.
2000 x 1800 = 3600000 J.
22.What is the National Grid?
The system of cables and transformers that links power stations to consumers across the country.
23.What does a step-up transformer do?
It increases the potential difference and decreases the current for transmission.
24.Why is the current reduced for transmission?
Energy is dissipated in the cables in proportion to current squared, so a smaller current wastes far less energy.
25.What does a step-down transformer do?
It reduces the potential difference to a safer, usable level before electricity reaches homes.
26.Why is high potential difference transmission efficient but dangerous?
It greatly reduces energy loss in the cables, but the very high potential difference would be lethal, which is why it is stepped down before use.
27.Why does a higher current cause more energy loss in a cable?
The cable has resistance, and power dissipated equals current squared times resistance.
28.What energy transfer happens in a resistor carrying a current?
Energy is transferred electrically and dissipated to the thermal store of the resistor and surroundings.
You remember far more by trying to recall an answer than by reading it. Run these as flashcards and the ones you keep getting wrong will come back more often.
Start studyingOr see the other Electricity decks.