How a torch works



Switching on a torch
Imagine you are walking home at night and you drop your key. It is dark on the ground and the key cannot be seen. Fortunately you have a torch and you switch it on.
Inside the torch electricity flows from the batteries and around a circuit. This idea is shown in the diagram below.

There is a bulb in the circuit and as the electricity flows through it, the bulb filament shines. The light from the bulb spreads out in all directions. Some of the light strikes the curved shiny surface around the bulb. This surface is called the reflector. The light that strikes the reflector is reflected in such a way that it forms a beam which makes a bright disc of light on the ground. Now it is easy to find your key.
As you can see from this example, a torch has many useful features for helping you see in the dark:
1. It is portable and can be taken anywhere.
2. The torch is made of light weight materials which makes it easy to carry.
3. It has a shape which is easy to hold.


Why is the bulb connected directly to the battery?
A wire is not needed as the base of the bulb is metal just like the wire, and electricity can flow through it into the filament.

How is the bottom of the battery connected to the bulb?
A long strip of metal is used. One end of the metal is connected to the spring and the other end touches the bulb. A slider switch is placed in the middle of the strip so that the torch can be turned on and off.
Why does the battery have a spring?
It has a spring to push the two batteries together. If they are not kept together a gap may form between them and this would stop the flow of electricity. The spring is made of metal and this conducts electricity from the switch to the batteries.
The spring is important because the torch is portable. A spring keeps the connection made firm even when the torch is dropped. Using a spring also makes it easy to change batteries.


How is a pen torch different from an ordinary torch?
It does not have a reflector but has a bulb which has a lens in its top. This makes the light from the bulb form a beam. Find a pen torch and check it out.