I predict, as the wire increases in length so will the resistance because of the pressure of the electrons trying to get through the wire. As the wire increases in length the ability of the wire to stop melting will decrease because of the voltage in the circuit.
To male the experiment a fair test I will repeat each test on the length of wire three time so that I can find an average of the resistance in the nichrome wire. Ohm’s law states that for a fixed voltage applied to a different conductor there will be a different amount of current flowing through each different conductor.
Equipment I will need include, connective wires with crocodile clips, protective glasses, power supply of 3 volts, an ammeter, a voltmeter, pen, paper, 100 meter rule, nichrome wiring (upto 1000mm), main electricity supply and a calculator.
Results
When I did the experiments I wore protective glasses because of the wire melting and being able to burn my skin. When I made up the circuits I set it out like this:-
Here are the results from my first experiment:-
Here are the results from doing the experiment a second time:-
Here are the results from doing the experiment a third time:-
For the third experiment when I switched on the power supply the readings for the current were different. In the first two trials the current was the same but for the third trial the current came up with a different answer. To get around this I kept on turning the power supply on and reading the ammeter until it came up with the same readings in the first two trials. In the third table the numbers with the * next to the resistance showed where the anomalies were, when I tried it out again I did get the same number. When I draw my graphs, I will not use the three results I got on the first trial but I will use the results I got from the first and second trial. Hopefully then my graph will obey ohm’s law by “the current through a metallic conductor is directly proportional to the potential difference across its ends if the temperature is constant.”
Conclusion
From the results I got from doing the experiment I was able to see that as the length of the nichrome wire increased in length, the resistance of the wire also increased. As the length of the wire increased in length the current that was able to pass through it decreased because of the resistance stopping the electrons to pass though the circuit. The voltage increased very slightly as the length of the wire increased also. As the current decreased, the voltage increased.
This graph compares how the length of the wire in each experiment affected the resistance in the circuit. From drawing this graph I am able to see as the length increased so did the resistance. Ohm’s law says “the current through a metallic conductor is directly proportional to the potential difference across its ends if the temperature is constant.” By the results I got from my experiment it shows that the resistance in the wire followed ohm’s law and that a straight lined graph was produced. Trends and patterns I noticed were that as the as the length increased by 100 mm the voltage increased very slightly. For 100 mm the voltage was 0.10 volts and then when I used a 200 mm piece of wire the voltage increased quite a lot to 0.34. For the rest of the results each time the length of the wire increased by 100mm the voltage increased by 0.01 or 0.02. The reason that the voltage increased slightly was because there the circuit needed more push so that the current was able to flow through the resistance.
The graph on the next page shows how the current and the voltage is affected by the length of the wire. As the length of the wire increases the voltage does too and the current decreases. This is because the longer the wire, the more compact the space is inside which results in the electrons being squeezed together and causing the current to decrease.
From the graph comparing how current and voltage is affected by the length of the wire I am able to see that as the voltage decreased (length of wire was increasing), the current passing through the circuit decreased.
Evaluation
The procedure of finding out whether ohm’s law worked on the length of nichrome wiring was a good method and the test did show that the wire obeyed ohm’s law. The wire was quite hard to straighten out properly so when it came to measuring it out to the nearest millimetre it was quite accurate, but the difference In the length had to be spot on to obtain correct results. When I wrote down what to do for this experiment I should of made it more specific that the other variables could not changed and that they had to stay the same.
When the power supply was switched on, I could only leave it on for a few seconds and take a quick reading from the ammeter and the voltmeter. This was because the wire was very thin and the voltage was quite high for the thickness of the wire and so it would melt very easily. If I left the power supply on then the voltmeter reading would start to decrease because of the resistance in the wire increasing. This would show anomalies in the results so I had to switch on the circuit for only a few seconds and re-take the test three times to make sure I was writing down fair and accurate results.
Ways in which I could improve the experiment is before I actually do the tests on the different lengths of wire, test out three different lengths and just see what sort of results I was likely to get from the experiment. This would help me see of the experiment was going totally wrong and if the resistance was decreasing instead of increasing and the wire length got longer.