Practice Assignment 09
Comparing electrical properties of metals
Connecting wires shouldn’t get hot. But some wires, like filaments in lamps, are meant to get hot. The resistance of a wire affects how hot it gets.
The resistance of a wire depends on how long and how thick it is. It also depends on what metal it is made of. So it’s important to compare how different metals behave. Then you can decide which metal to use for a particular electrical purpose.
Your task is to produce a bar chart to compare different metals.
What you have to do
- Get a copy of the Standard Procedure SP 0009:2005 Measuring the resistance of metal wires.
- Before starting:
- read the standard procedure and the hints below carefully
- check that a risk assessment has been carried out
- list the equipment and materials that you need.
- Use the procedure to measure the resistance of 1 metre length of a wire.
- Repeat this for 1 metre lengths of two more wires made of different metals. Check that all of your wires have the same thickness as well as the same length.
- Present your results as a list or table.
- Make a bar chart to show the resistances of the different metal wires.
Some hints
Remember: Write up your results in your Laboratory Notebook.
- You need to make connections to your wire with crocodile clips. You can measure the distance between crocodile clips using the centres or the sides of the clips. The important thing is that you do the same for all three wires.
- The wire may be more than 1 metre long, provided your voltmeter connections are 1 metre apart.
- Ammeters measure electrical ‘flow’ or current. Voltmeters measure the electrical difference that provides ‘push’. You have to connect the ammeter into the main loop of the circuit. The voltmeter does not go into the main loop. So, the easiest way to set up your circuit is to make the main loop first. This connects together the cell (or battery), switch, ammeter and specimen wire. Then connect the voltmeter to the crocodile clips at the ends of the specimen wire.
Some questions
- Why should all the wires have the same length and thickness in this comparison activity?
- The resistance of a specimen of wire is equal to the voltage that’s applied to it divided by the current that flows through it. The Standard Procedure sheet gives a formula. Make up a memory aid (mnemonic) for remembering the formula.
- Resistivity is defined as:
resistivity = resistance x cross-sectional area
length
Explain which metal has the highest resistivity and which metal has the lowest. - Find out where you could buy a selection of wires with different resistivity.
- Find out the resistivities of several different metals. Make a list of at least four of the values you find.
- Look back at what you have done. Suggest what you could have done better.