There is not much resistance in the pin, and so it allows the electricity to rush through it. People sometimes cause fuses to blow out by pinning pictures to electric lamp wires or by pinning the wires up out of the way.
A short circuit an "easy circuit." You always get a short circuit when you give electricity an easy way to get from one wire to the other. But you get no current unless you give it some way to pass from one wire to the other, thus completing the circuit. Therefore you should always complete the circuit through something which resists the flow of electricity, like an electric lamp, a heater, or an iron. Remember this and you will have the key to an understanding of the practical use of electricity.
The term "short circuit" is a little confusing, in that electricity may have to go a longer way to be short circuited than to pass through some resistance, such as a lamp. Really a short circuit should be called an "easy circuit" or something like that, to indicate that it is the path of least resistance. Wherever the electricity has a chance to complete its circuit without going through any considerable resistance, no matter how far it goes, we have a short circuit. And since everything resists electricity a little, a large enough flow of electricity would even heat a copper wire red hot; that is why a short circuit would be dangerous if you had no fuses.
Application 59. To test your knowledge of short circuits and fuses, trace the current carefully from the upper wire as it enters the laboratory, through the plug fuse. Show where it comes from to enter the plug fuse, exactly how it goes through the fuse, where it comes out, and where it goes from there. Trace it on through the cartridge fuse in the same way, through all the switches into the lamp socket, through the lamp, out of the lamp socket to the fuse gap, across this to the other wire, and on out of the room.
It goes on from there through more fuses and back to the dynamo from which the other wire comes.
Test yourself further with the following questions:
1. Where in this circuit is the resistance supposed to be?
2. What happens when you put a good conductor in place of this resistance if the electricity can get from one wire to the other without passing through this resistance?
3. Why do we use fuses?
4. What is a short circuit?
5. What makes an electric toaster get hot?