Circuits that will and will not work


You need connections to both ends of the battery.
The top diagram shows a circuit which will not work even though most of it is set up correctly. The batteries are facing the same way, the bulb is held firmly in its holder and the wires are connected to the contacts. This is all fine.
However, both wires are connected to the same terminal. This arrangement is not correct and a current of electricity will not flow.
In the lower diagram one wire is connected to the metal cap of one battery and the other is connected to the base of the second battery. This is the correct arrangement for using two batteries. All the other features of the circuit are correct so electricity will flow through it and the bulb will light.

What will happen if there are loose connections in the circuit?
The light bulb may not come on or may flicker when you move the wires. This is why you need to make sure that all of the components are connected firmly together.

What is wrong if bulbs only glow weakly?
There are several reasons for this:
1. The chemicals in the battery may be almost used up (battery is said to be 'run down'). However, don't be in too much of a hurry to throw the battery away until you are sure it's the battery that is at fault.
Before you throw the battery away make the following check. Try the battery with other bulbs that have been seen to glow brightly with other batteries. If they also glow weakly then you should replace the run down battery with a new one.
2. The batteries may not match the bulb. Look carefully at the bulb and find out its voltage. Then check the voltages of the batteries. For example, if you have a 3V bulb and are using just one 1.5V battery, then the bulb and battery do not match and the bulb will glow weakly. You will need to add another battery in line with the first one.

What is wrong if a bulb fails to light?
There are several reasons for this. You have to check each one in turn.
1. There may be a loose connection somewhere in the circuit.
2. The bulb may be broken.
3. The switch may be off.
4. The battery may be run down.
Make a check by replacing the bulb with another one that is known to work. If this bulb fails to light check all the connections. If the bulb lights. the first one may be broken or be making a poor connection in its holder.
Then check the battery and the switch - as a rule of thumb, when anything in a circuit fails to work always check that you have got the circuit switched on!

Mains circuits in the home
Is there just one wiring loop in a home ?
No. There are at least two circuits and usually several circuits. For example, if you live in a house there may be a circuit connecting the plugs for the ground floor and a separate one for the first floor.
There may be separate circuits for the ceiling lights. The water heater, oven and shower may each have a separate circuit.
The wires are shown in the diagram below. This may look complicated, but the wires are really only in simple loops. Check this out for yourself by looking at the loop circuit for plugs on the diagram.


Where are the wires in the circuits in the home?
They are hidden in the walls and ceilings. If you look at the plugs in a room imagine being able to see through the wall, then in your mind follow the wires from one plug socket to the next.
If you look at a light switch imagine the wire going up the wall to the ceiling then across the ceiling to the lights.

Where does the electricity come from to flow round the circuits in a home?
It comes from a power station which may be many kilometres away. The electricity may have travelled on overhead cables across the countryside but in a town it will have travelled in an underground cable.