Electric Circuits

Simple Circuits

---

When we use wires to connect a battery with a bulb (or buzzer etc) and the bulb lights then we have a circuit

The inside of a wire is made of COPPER (which is a good conductor of electricity)
The copper wire is covered with coloured plastic (which is an insulator).

Example Here is a circuit where a battery (sometimes called a cell) is connected to a bulb using wires. Below is a circuit diagram of the same circuit using the correct symbols

The Cell  Circuit symbol The cell has a voltage which makes an electric current flow around the circuit. The higher the voltage the greater the current A 'battery' of cells Symbol for a battery Several cells joined together form a battery.

The bulb

Circuit symbol

The BULB

A light bulb has a thin metal filament, often made out of tungsten, which glows very hot when an electric current flows through it. If we use a higher voltage more current will flow and the filament gets hotter and glows brighter. Too much current makes the filament melt (and the bulb ‘blows’).

How to join a bulb:

Circuit diagram Two bulbs joined end to end (in series) This is how christmas tree lights are joined together If one bulb is unscrewed the other bulb will also go out

Circuit diagram Two bulbs joined side by side (in parallel) This is how the lights in a house are wired together. If one bulb is unscrewed the other bulb will stay alight

Changing the brightness of a bulb 

Circuit diagram Two cells makes the bulb brighter because there is a higher voltage

Circuit diagram Two bulbs (in series) makes the bulbs dimmer because it is more diffcult for the electricity to flow

Making the wire longer will make the bulb dimmer

Circuit diagram Two cells and two bulbs is the same brightness as one cell and one bulb

Using a switch

Circuit diagram All the switch does is to break the circuit and switch everything off (or on) It does not matter where we put a switch in the circuit. A switch like this is sometimes called a SPST switch ( SPST=Single Pole Single Throw)

Sometimes a circuit does not work.

The three main causes for a circuit not working are:

• A wire not connected (or broken)
• The bulb 'blown'. This is when the filament has melted.
• The batteries are dead (flat)

There is something wrong with each of the circuits below. can you see what it is? (Hold your mouse over the diagram to find out)
source :http://www.mikecurtis.org.uk