An electric iron has a metal body and a three-pin plug.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
An electric iron has a metal body and a three-pin plug.
- What is the third pin for?
- A fault joins the live wire to the body. The path through the earth wire has a resistance of . What current flows to the earth? Will a fuse melt?
- What could happen if the earth wire were missing?
Need a reminder? The key ideaShow
House circuits are in parallel at , with a live, a neutral and an earth wire. The current of an appliance is , and the currents add up. A fuse in the live wire melts when the current is too large (a short circuit or overloading). The earth wire joins a metal body to the ground.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The third pin joins the metal body to the earth wire, and so to the ground.
Step 2. (b) . This is far more than , so the fuse melts at once and cuts off the supply.
Step 3. (c) The body would stay at . A person who touched it would become the path to the ground and get a severe shock.
Answer: it earths the body; , and the fuse melts; a shock, perhaps a fatal one.
Check. In normal use the earth wire carries no current at all.
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