Mains Electricity Quiz
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5 questions, one answer each
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1. What is the key difference between direct current and alternating current?
- A. D.c. changes direction repeatedly; a.c. flows in one direction only
- B. D.c. flows in one direction only; a.c. changes direction repeatedly
- C. Both flow in one direction, but at different speeds
- D. D.c. only exists in batteries, a.c. only exists in the human body
2. What are the approximate frequency and voltage of the UK domestic mains supply?
- A. 60 Hz, 120 V
- B. 50 Hz, 230 V
- C. 100 Hz, 12 V
- D. 50 Hz, 12 V
3. Why must a fuse be connected in the live wire rather than the neutral wire?
- A. It makes no difference which wire the fuse is in
- B. So the appliance is disconnected from the dangerous live supply if the fuse blows
- C. Because the neutral wire cannot carry a fuse
- D. Because the live wire never carries current
4. A fault causes the live wire to touch the metal casing of an appliance fitted with an earth wire. What happens?
- A. Nothing, because the earth wire is disconnected by design
- B. A large current flows through the low-resistance earth wire, blowing the fuse or tripping the circuit breaker
- C. The neutral wire immediately melts
- D. The appliance casing becomes permanently live with no protection
5. Why is touching a bare live wire dangerous, while touching a bare neutral wire is (relatively) much safer?
- A. The live wire is at a high alternating potential difference relative to earth, while the neutral wire is at approximately 0 V
- B. The live wire never carries current, unlike the neutral wire
- C. The neutral wire is always disconnected from the circuit
- D. Both wires are equally dangerous at all times