Electricity 1

Basic Circuits


Everyone finds Electricity fascinating even though it may be difficult to understand at times.

In order to make successful circuits you must get organised and try to keep things neat and tidy otherwise it is very easy to get mixed up and difficult to see where things are going wrong.

A jumble of long wires tangle up on the desk is a bad way to introduce the topic of electricity.

A common mistake which prevents all circuits from functioning is to allow ‘short circuits’. This is when the bare ends of wires or croc. clips touch where they are not supposed to and allow electricity to flow along a path leading directly back to the battery - this quickly flattens the battery and spoils further circuits.


A great start is to arrange a battery and two short croc. clip wires so that they always stay in one place and the two end croc. clips are too short to touch one another.

Always start a circuit like this and finish like this
at the end of a lesson.

Here two fasteners have been used to pin down the wires on a foam base in a plastic carry case.


A switch and bulb have been connected to the battery so that the switch can control the flow electricity. The switch allows the circuit to be ‘completed’. Electricity can only flow along a path made from conducting materials (more about this later). We call this a complete circuit.
Switch off.
Try disconnecting the bulb, turning it round so that the croc. clips connect to the opposite terminals and switch on. This simple change is important and tells us that it makes no difference to a bulb which way around we connect it in a circuit. Try this with the switch and then try swapping the positions of switch and bulb.


How does a switch work?

Try using some paper fasteners to make a switch and this will hep explain what is inside a switch and how it ‘makes’ and ‘breaks’ a circuit.

An important thing to note is that paper fasteners are made from a metal. Metals are important in circuits and switches.

Here is an excellent way to make a switch.

One fastener has been pushed into the foam base and is connected to a croc. clip wire. The other fastener has had one leg bent outwards and the other pushed into the foam and connected to another croc. clip.

Push down on the raised up leg and this makes it touch or ‘make contact’ with the other fastener.

This completes the circuit and makes the bulb light up. Switches contain a fixed and a moving metal contact which together can complete a circuit. We provide the force to make the contacts close together.

When we know some science it’s great fun to invent and solve problems.

How do ships at sea at night know which lighthouse they are approaching? Ans. each one has its own special sequence of flashes.

Flashes of light have been used to send messages for thousands of years eg. reflections from a soldier’s shield or signal fires in ancient times.

We can send messages using Morse Code.

A better way to send Morse Code messages is using a buzzer but we need to find out something about the buzzer first.

In this circuit the buzzer has replaced the bulb but it does not work.

Have a close look at the colour of the buzzer wires.

Buzzers are not like bulbs - they will only work one way round in a circuit and the red and black wires help us tell which way to connect them.

Have a close look at the battery also.

It has a plus (+) mark at one end and a minus (-) mark at the other.

The red wire of the buzzer must connect to the plus terminal of the battery or it will not work.

This is why it was important earlier to try the bulb and switch in different orientations. All ‘components’ are not the same and assumptions can lead to confusion.

Things to try

1. With the buzzer and paper clip switch in the circuit try sending a Morse Code ‘bleep’ message. You will have to practice a short bleep and slightly longer bleep so that you can tell the difference between a dot and dash in the code.

A dot    .   is a short ‘bleep’

A dash   ___    is a long ‘bleeeep’

When writing Morse code a forwardslash character / means a pause between two letters in a word.

eg. What is this word?       . . . . / . / . _ . . / . _ . . / _ _ _


morse code 102

Try writing your name in Morse Code and send it as a message

Tom          _  / _ _ _  / _ _

Think of a secret code word and send it to a friend to see if they can guess what it is.
My code word is

. . .  / _ . _ .  / . .  / .  / _ .  / _ . _ .  / .

Circuit symbols and diagrams

elec circ 1

Scientists and Engineers have a special way of drawing an electrical circuit.

They use special symbols which everyone, all over the world, uses to represent the components.

Just as the real components can be linked together to make a circuit that works, we can link together the symbols to make a complete circuit diagram to represent a circuit.

elec circ 1a

It is important to take your time and gradually work your way around a circuit diagram so that you understand which components are present and how they are connected.

Look at the two circuit diagrams above. Are they the same? Will both circuits do the same thing or will they do something different?

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