Teacher information

Go to make an electric circuit online: Voltage, Current, resistance

The Voltage, Current, resistance was written for children learning about Ohms Law, although other ages may find it useful. It is an interactive webpage. This means that you can build up a circuit on the screen with various resistances, and measure the current and voltage drop in various places. You can choose a simple circuit or a parallel circuit.

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. If you select a parallel circuit, you will get another circuit off part of the first circuit. You can then add extra components to this.

Voltmeters are rather more complicated. You need to specify two places for the voltmeter to show the voltage drop between the two points. So select the voltmeter, click in the first place, then click in the second. If you only specify one point, then it won't work. Only one voltmeter is allowed in a simple circuit. For a parallel circuit, you can have two voltmeters, one measuring a voltage drop anywhere on the top part of the circuit and the other measuring a voltage drop only on the bottom part of the parallel circuit.

When you think the circuit is complete, close the switch in the circuit by clicking on it. This will run the circuit, and the ammeters or voltmeters will show a value. If there is a short circuit, you will be told about it! The ammeter and voltmeter give values to 2 decimal places. This might lead to rounding errors.

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 by selecting the second one, then clicking on top of the first one. If you just want to delete a component, then select the 'delete' (which is just a piece of wire) and click the component.

There is a quicker way to delete or move a voltmeter. Select the voltmeter. Then if you click on an existing voltmeter, it will disappear. Then you click on a new place and it will reappear. This means that you can move voltmeters quite quickly.

Components

• Resistors of various values - A resistor changes the amount of current flowing in the circuit.
• Ammeter - Measures how much current is flowing at this point.
• Voltmeter - Needs to be set up in two places. Measures the voltage drop between the points.
• Delete - a piece of wire. Select this to delete a component if you don't want to replace it with another.

The symbols are close to the official symbols. The Voltmeter is different as I wanted to make it obvious how to set it up and move it.

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. The idea of these circuits is to demonstrate Ohms law:

V = I R

Voltage = Current x Resistance

plus the ways of combining resistances:

Simple circuits: RT = R1 + R2

Parallel circuits: 1 / RT = 1 / R1 + 1 / R2

So you can set up simple tasks, such as:

• Putting various resistances in a simple circuit, putting in ammeters at various points, and seeing that they give the same current.
• So you only need one ammeter for a simple circuit (which is supplied). Now try different combinations of resistances, and see that, for example, two resistances of 2 ohms each are equivalent to one resistance of 4 ohms. Carry on playing with different values until they can deduce how resistances can be combined for simple circuits.
• Can they work out the relationship between voltage (which is 6 volts for the whole circuit), current and total resistance?
• Now add a voltmeter across various points, and work out the voltage drop over various amounts of resistances, considering the current.
• You can now add a parallel circuit. Combining resistances across parallel circuits is trickier, so they might need some clues! It might be easier to start by only having resistances in the truly parallel parts of the circuit. The parallel circuit is deliberately set up so parts are in series and parts are in parallel. So you can start with simple ideas and move to more complex ones.
• Put an ammeter in each part of the parallel circuit. You should find up to three different amounts of current flowing in the different parts. Why?
• Now try put one or two voltmeters in to see if they can understand why the voltage drop is what it is.

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: Voltage, Current, resistance