S4.12.8 For the adult
Mains electricity and safety
Hana can take a torch apart, but she must never take apart a plugged in lamp. What is different about the mains?
What this chapter teaches
A cell gives direct current. The mains gives alternating current, which reverses many times a second. Its p.d. and frequency differ from place to place. The live wire carries the supply, the neutral completes the circuit and the earth wire is a safety wire. The fuse melts in a fault. Mains is never used for experiments.
Three questions to ask
There is no one right wording. Listen for the idea.
- What is the difference between direct and alternating current, and which does a cell give?
- What are the jobs of the live, neutral and earth wires, and why does the fuse go in the live wire?
- Why can a torch cell be taken apart but a plugged in lamp never be?
After the chapter, the learner can
- Explain the difference between direct and alternating current
- Explain the jobs of the live, neutral and earth wires and the fuse
- Explain why mains electricity is never used for home experiments
What they copy into their notebook
d.c. one way, a.c. keeps reversing. f = 1 ÷ T. Live: supply. Neutral: return. Earth: safety. Fuse in the live wire. Mains can kill: use cells only.