What is a short circuit?
A simple, well-designed circuit, as discussed earlier, has a cell providing current along a path (wire), to a load (resistor) and back to the other end of the cell as shown in this diagram.
As the voltage gets to the resistor (load), there is a power drop, because the resistor uses some of the electricity up to produce heat and light. This means that the voltage that ends up at the other side of the cell is reduced.
In a short circuit, there is no load. For many reasons, the wires in a circuit can find a short-cut, bypassing the load (and other components). This causes the same voltage from the cell to flow to the other end of the cell. When this happens the high voltage causes the wires to heat up and catch fire.
Can you think of some reasons why there could be a short circuit?
Here are a few:
Wires may loose their insulation and touch each other in the circuit
There could be a fault (improper wiring) in a device
Intentionally connecting both ends of a cell / battery with wires. This causes a massive drain of electricity and the battery looses its power in a very short time.
A short circuit can cause heating, melting of wires, harmful smoke and smell, and blinding light (like what you see during welding)