To make it a fair test the thickness, temperature and type of wire will be kept the same and voltage will be kept at setting 2 as in the 1st experiment. The main reason for using crocodile clips in this experiment is because (as well as the reasons mentioned in the 1st experiment) they can slide easily up and down the wire, making It easy to record the results at different lengths. Safety Using a low voltage setting (2v) will ensure maximum safety, by preventing over heating of the wire and possible burns on the skin and/or sparks.
Prediction
I predict that the longer the wire the higher the resistance will be, because the electrons will encounter more obstruction when flowing through, the atoms of the wire will be like a blockade and the longer the blockade the harder it will be for the electrons to squeeze through the gaps.
Apparatus
- Crocodile Clips; to attach the wires to the metal being tested.
- Battery Pack; to supply the power for the circuit (voltage setting 2).
- 5 Wires; to allow the electrons to flow in a complete circuit.
- Ammeter; to measure the amps.
- Voltmeter; to measure the volts.
- Meter Rule with different wires; depending on which experiment.
1st experiment Method
- Firstly assemble the circuit as shown in the diagram of apparatus using one type of wire at a time (you can start with any wire). The length of each wire however must be kept at 30cm.
- When the circuit is complete turn on the battery pack to voltage setting 2.
- Let it run for about 5 seconds while the readings fluctuate then record the amps and volts.
- Turn off the battery pack for about 30 seconds switch it back on a record the results again.
- Then once more turn off the battery pack let it cool and switch back on and record the results. You should now have three very similar results for one wire.
- Repeat numbers 2 – 6 for all four wires.
- Using the three results for each test make an average current and voltage for each wire.
- With these results you can work out the resistance by using the following equation: V/I = R Where current is I, voltage is V and resistance is R. The wire with the most resistance will be used in the following experiment.
2nd experiment Method
- I will Begin the experiment with a similar set up to the 1st experiment, only the wire I’m going to test does not change.
- Record the voltage and current for the first length (10cm), after recording the results switch off the battery pack, let it cool for about 30 seconds.
- Whilst the battery pack is cooling move the crocodile clip along the length of the wire to the second interval (20cm).
- Carry on moving the crocodile clips along the length, letting the battery pack cool and recording the volts and amps until you have the readings for all 10 intervals (100cm).
- Repeat this test a further 3 times, and make an average of all three measurements for each length.
- Using the averages for the amps and volts work out the resistance of the wire at each length (the formula is shown above).
- Use this information to plot a graph, length against resistance and evaluate. For all the results the decimals are rounded to two decimal places.
The electrons are freed from the battey that is slowly deteriorating letting more and more electrons free, they move from negative to positive – the opposite direction to conventional current (the direction people thought electricity would flow). The highlighted metal, (constantan) is the metal I’m going to use in the second experiment. Ideally I would use Nichrome but there is a shortage of supplies so we couldn’t obtain a length of Nichrome wire so Constantan is the second best as it has the second highest resistance.
The testing for this experiment was sound; no faults were recorded because we had 3 sets of results making the results very accurate when getting an average the results for each test were also very similar anyway.
Improvements
Although the averages were correct, I feel that in some parts of the tests we did not leave the wire to cool for long enough and so the resistance was amplified, next time I do the experiment I will leave the wire to cool for exactly 30 seconds and set a stop watch to records this. Another way of preventing the wire from overheating is by attaching a light bulb to the circuit to absorb the heat.
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