Adding to the loop


Looking at a loop

The golden rule in all simple electrical circuits is to know that they make a loop, or ring. Once you know this, it's much easier to wire things up correctly.
Now we need to know how many working parts, or components, we can put in our loop. This is a simple matter of adding up the numbers on the battery or batteries and then adding up the numbers on the bulbs. If the numbers on the bulbs add up to the numbers on the batteries, then all is well. If they don't, then we must do something about it.
This first activity helps you to understand what happens when a mismatch occurs.


What happens when you add more and more bulbs to a circuit?
The bulbs get dimmer and dimmer. Eventually they will not glow at all.
Why do the bulbs glow less brightly?
When a current of electricity passes through a filament it has to push its way through the metal. Some of the energy of the current is used in this push. When two bulbs are used in a series circuit the current uses up twice as much energy in pushing through the filaments so it has less energy left to make the filament glow. This results in the two bulbs glowing more dimly than the single bulb.


When batteries are added in series can they be put anywhere in the circuit?
No. They will only give a higher voltage if they are placed directly in line.


What happens if something breaks in a series circuit?
If something breaks to stop the flow of electricity the current stops and all the components stop working. If you have a switch and a bulb in series you close the switch to let the electricity flow through the circuit and the filament lights up. If you have a series circuit with two or more bulbs and the filament of one bulb breaks it behaves like a switch being turned off, stopping electricity flowing through the circuit. When this happens all the bulbs go out.

Can making and breaking a circuit be useful?
Yes. It gives complete control to the flow of electricity. The switch is the component that is used to make and break circuits. When the switch is open the circuit is broken and the current cannot flow. When the switch is closed the circuit is completed and electricity flows. You should always switch off circuits that you are not using to save electrical energy.
You will find that many electrical devices have automatic switches in them. The older forms of bells and buzzers are like this. By switching the current on and off quickly, hammers were made to hit bells quickly and so produce a ringing sound.

Can a motor be used with any battery?
No. Motors, like other components such as bulbs and buzzers, work best at a particular voltage. If the voltage of a battery is too low the motor will not work but if it is too high the motor will burn out quickly.