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Introduction to electricity

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Index --- Introduction to electricity --- Voltage, Current, Resistance


Go to make an electric circuit online: Introduction to electricity


The Electric Circuit webpage was written for Primary School children, aged 7-11, although other ages may find it useful. It is an interactive webpage. This means that you can build up a simple circuit on the screen. The page will tell you if the circuit will work. You can turn the switch on, turn lights on and off, make the motor run, flash the light, and investigate simple facts about electric circuits.

The page does not measure current or voltage explicitly. If you want a circuit with ammeters or voltmeters, click here.

Setting up the circuit

To start with, you make a circuit by clicking on items, and putting them in the circuit by clicking on the grey part of the wire. (The battery and wire position themselves automatically.) When you think the circuit is complete, close the switch in the circuit by clicking on it. The webpage will inform you of any errors. These may include:

This high-lights important facts about an electric circuit. However, to save time, you can select 'Complete simple circuit'. This will give you a working circuit with a light-bulb and the switch off.

Changing the circuit

You can then change the circuit and observe the results. You can turn the switch off (by clicking on it) and on again. To add or replace components, select what you want by clicking on the item, and click where you want it to go in the circuit. You can replace one component by another, or delete a component.

If you select a parallel circuit, you will get another circuit off the same battery. You can then add extra components to this. You can have up to three parallel circuits, including the first one. Remember that you need at least one component on each circuit to avoid a short circuit.

Components

The symbols are close to the official symbols. The light bulb symbol is not conventionally grey, but I wanted to make it look dimmer off than on. The dead light bulb and the flashing light bulb are definitely not official. The resistances are again close, but all resistors should have the same symbol, with the resistance value written by it. I have used slightly different symbols for the two resistors instead. This website is for young children, and I wanted to avoid any mention of numerical values for current, resistance or voltage (see below).

The two resistors are there to experiment with different values of current. The light bulbs (apart from the dead one!), the motor and the medium resistor all have the same value of internal resistance. This makes the sums easier! The high resistor has twice the resistance. This means that a high resistor in series with a light bulb makes it go dimmer than a medium resistance in the same circuit. This can be used as a very simple introduction to Ohm's Law (see below).

How to use the webpage

How you use the webpage is up to you. You could let children loose on it and see what they discover for themselves or you could give them very controlled tasks to carry out. Here are some ideas for challenges:

Simple circuit
  • What happens if you have one light? Two? Three?
  • What happens it you have a flashing light bulb and an ordinary light?
  • What happens if you have a flashing light bulb and a motor? Why?
  • How can you get one dim light bulb?
  • What happens if you have a motor and a resistor? Is it different for a medium resistor and a high resistor?
  • What happens if you have a dead light bulb in series with an OK light bulb?
  • What happens if you put an extra switch in?
Parallel circuits
  • What happens if you have no components on one line?
  • What happens if you have one light on each line?
  • What happens if you have one light on one line and two on another?
  • What happens with a flashing light on one circuit, two on a second and three on a third?
  • Can you get 3 lights that switch on and off independently?
  • What is the most complicated circuit you can make? Why is it behaving like that?

The Science Bit!

Nothing will happen unless you have current flowing. For current, you need a battery. You also need a complete circuit This means not only wire from the battery to the component (such as a light bulb) but also wire back to the battery. A switch works by breaking the circuit, which stops the current. When you turn it on (or close the switch) this completes the circuit again so current will flow. A dead light-bulb is a break in the circuit, so that will also stop the current.

The fundamental formula for electricity is Ohm's Law, which states

V = I R

Voltage = Current x Resistance

Voltage comes from a battery and these circuits all have one battery, so they all have the same voltage. This means that the more resistance you have in these circuits, the less current. The light bulbs are a very simple measure of current. More current means a brighter light bulb. It recognises four levels of current:

high = bright (yellow)
medium = medium (orange)
low = dull (red)
none = no light (grey)

You may get no light because the resistance is too high, making the current too low to make the light bulb work. Every component (apart from the switch, the wire and the dead light bulb) has a resistance, including the ordinary light bulbs. So the more light bulbs or other components you have in a circuit, the more resistance, the less current, the dimmer the bulbs.

Current is the same throughout the whole of a simple circuit (very clever of electricity this, how does it know?) So all the light bulbs in a simple circuit are the same brightness (or dimness). To make things a little easier, all components have the same resistance, except the high resistance resistor, which has twice the resistance. So the only way you can have too much resistance to make things work is to use the high resistance.

Parallel circuits are several simple circuits using the same battery. Each line acts as a separate circuit, independent of the others. The top line is in all of the circuits, but the webpage only allows the battery and the main switch here. (This is to stop the circuits from getting too complicated.) Each circuit has its own current, which may be different, leading to different brightnesses of bulbs. It may seem strange that three bulbs in series are dim, and three in parallel are bright, but these will run the battery down quicker, as they are drawing more power from it. (This doesn't happen on the webpage!) You can even have no current flowing in one part of the parallel circuits, by using a switch or a dead light bulb or too high a resistance, while there is plenty of current in a different part. Click here if you want to experiment with more complicated circuits with componenets both in series and in parallel.

An electric motor basically goes round and round. Think of an electric kitchen blender or fan. It will go round faster or slower depending on the amount of current. Electric motors are used in many ways, but this webpage just shows the letter M rotating!

The flashing light bulb is a bimetallic strip. These used to be common in Christmas tree lights (unfortunately modern ones work in a different way). A bimetallic strip is two strips of different metals fastened together. They expand at different rates when heated. The strip rests on a contact. When the bulb is switched on, it heats up, and one part of the strip expands faster, so the whole strip bends away from the contact. This switches the bulb off. But that causes it to cool down, the strip straightens out again and touches the contact again, and the light is switched on again, which causes it to heat up... hence the flashing. I included flashing light bulbs partly for fun (every adult who tries this webpage plays about with them!) but they do demonstrate an interesting idea.

The dead light bulb is another piece of fun. If a light bulb breaks, it acts like a break in the circuit, or a switch which is permanently off. Since you do get dead bulbs in the real world, especially in school electrical kits, I added one to our web kit! It does demonstrate that a break in the circuit stops the current.

I have already mentioned that all components have a resistance. But what happens if you have no resistance in a circuit? If you feed zero resistance into the formula above, you will find that you need infinite current. In real life, you burn out the battery, blow a fuse, cause an almighty spark, in general break something! Webpages are much easier to control. But I do give a message if you have caused a short circuit in any of your circuits (since in parallel circuits you can have a short circuit in one part only). You then have to start with a new circuit (since you have probably burnt out the old battery!) This webpage allows children to play around with components and discover important ideas like short circuits without actually damaging any school equipment.

This webpage does not have bad connections. They're enough of a bother in real life. Also the battery doesn't run down. We have to leave something for the real world to demonstrate!

Please note that I don't necessarily think the above science to be necessarily appropriate for 7-11 year olds. They will meet these ideas later on. I have supplied this for any adult who is interested in why things are working the way they do. However, I know that children frequently surprise us with their grasp of ideas. So the webpage contains some logical concepts for children to explore. I would make a plea that the more advanced ideas are kept as fun - as answers to children's questions or experiments to be tried, rather than problems to be worked through or knowledge dinned into their heads.

Printing and saving the webpage

The circuit that you produce is not one picture. Every component is a different picture. This means that the quickest way to print off a circuit is to print the entire webpage using the Print button in the browser toolbar.

If you want to save the circuit in an electronic form, then press the PrtScn button on your keyboard (top right). This will copy what is on your screen into your computer clipboard as a picture. (This works similar to Copy.) You can then go into a word processor or a Paint program and Paste it in. This does reproduce the whole screen, complete with toolbars, so you may want to edit or crop the picture somehow.


Go to make an electric circuit online: Introduction to electricity