You will need
- Pens or pencils
- Scrap paper
- Calculator or phone
- A multimeter
- Circuits and circuit components, including crocodile clips and terminal blocks
Before you begin
- You will need some ready made circuits to test, either have some circuits ready or have all the components and equipment needed to make some. The circuits could be borrowed or reused from other sessions. You could save on circuits and multimeters by running this activity as a base, with groups taking turns to complete the tasks. They must not be mains powered.
- This is a good opportunity to invite an expert along to share their knowledge with the group. There are also lots of handy step-by-step videos on the internet (including ‘how to’ guides) about multimeters.
- Bear in mind that when using a 9V (volt) battery, any resistors used should be at least 100Ω (ohm) and that an appropriate current-limiting resistor (at least 330Ω) must be used for any circuits containing a light-emitting diode (LED).
- Use crocodile clips and terminal blocks to temporarily make circuits. Changing components, like resistors, should change the circuit values.
Run the activity
- Give out copies of the ‘Multimeter diagram’ sheet to everyone taking part.
- Share this information with the group. They might like to write the information shared throughout this activity on the back of their sheets:
- Switch on the multimeter and choose a resistance with the dial. Use the ‘Multimeter diagram’ for guidance. Check the stated resistance of your components and set the multimeter to read higher than the maximum resistance expected. Remember to disconnect your resistor from any circuits.
- Touch the probes together. This should make the meter read 0. Now, take the resistor and place one probe on each of its terminals.
- Check to see if the resistance reading you get matches the resistance value on the component. Try this out with some different resistors. Large resistors may need to be measured with a different setting on the multimeter, measuring in kilo-ohms.
- Now, put together or choose a circuit on which to test voltage. Set the multimeter to the Direct Current Voltage (DCV) part of the dial, at a higher voltage than the maximum value expected. Have someone ready to write down the volts for each circuit.
- Connect the black lead to the negative terminal of the battery. The red lead is your probe, which you should touch against different parts of the circuit to measure the volts. See what happens if you swap out the resistors for ones with higher or lower values.
- Now, put together a circuit to measure current. To do this, your multimeter needs to be made part of the circuit, so that it can measure the current as it flows through it. Set the multimeter to the current setting; the Direct Current Amperage (DCA) part of the dial. As before, set it to measure higher than the maximum current expected.
- Check that the multimeter is the right way around before sending power through the circuit. Have someone write down the reading in amps.
- Now, you can work out the resistance in the circuits you measured amps and volts for. This requires ‘Ohm’s Law.’ This states that resistance (R) = volts (V) ÷ amps (I). You can also estimate resistance by adding up the values (in ohms) marked on the resistors used in the circuit. Do this for however many circuits you worked with and compare your results.
Using a multimeter is a valuable skill, as it can measure a whole range of different properties in a circuit. Can anyone come up with a rhyme, mnemonic, saying or song to help them remember the steps needed to measure volts, amps and resistance?
If you were lucky enough to welcome an expert to your meeting, what did they do that made them an electronics buff? Were they an electrician or engineer? What practical uses did they have for the multimeter? Some might have been PAT testing (safety-checking appliances like microwaves and kettles) and domestic/commercial wiring.
Supervise young people, and only do science activities that are advised and age appropriate for your section. Test activities first, to make sure you’re confident you can lead them safely. Use protective clothing where necessary.
Remove any equipment you’re working on from the power source before you begin. Never assume the power circuit’s off – test it with a voltmeter (and then test it again to be sure).
Only connect power to a circuit once you’ve finished working on it and have checked your work. Make sure your circuit isn’t overloaded, and return any covers you’ve removed.
Make sure that all electronics equipment is properly grounded. Use the right electronics tools, and always replace damaged equipment (for example, replace cables rather than repairing them with insulating tape). Always have safety equipment including a fire extinguisher, basic first aid kit, and mobile phone nearby.
- Manufacturer’s guidelines
All vehicles will be different so always follow the manufacturer’s guidelines.