- The current
- Same type of wire
- Same thickness wire
- Room temperature
I need to keep these factors the same to ensure a fair test. The only thing that will change will be the length of the wire.
I will begin measuring the resistance at 10cm intervals, beginning with 10cm going to 100cm.
I will repeat the experiment and compare the two sets of results and find the average.
In this investigation a simple circuit will be set up to read the voltage and current when the length of the wire changes. The length will range from 10cm - 100cm (1m) with intervals of 10cm. Moving the crocodile clip across the wire on a ruler will change the length of the wire. I will use 0.50Ohms as any higher than this will cause the wire to overheat, which could become dangerous.
After measuring the resistance at each 10cm, the power supply will be turned off to prevent over heating. The circuit will be set up as shown above
Apparatus I will need are:
- Voltmeter
- Ammeter
- Crocodile clips
- Variable power supply
- Constantan wire
- Wires to connect the circuit together
- Metre long ruler
From my results, I can see that the resistance is proportional to the length, meaning that when one doubles, so does the other. An example would be at a wire length of 50 cm, the resistance is 3.38Ohms and at 100 cm it is 6.63Ohms. This is almost exactly double the size.
The results from the graph give a clear indication of how the resistance compares to the wire length. When the length of the wire increases, the resistance also increases.
The theory behind this is explained in the prediction. In any given metal wire, there are a number of atoms and free moving electrons. Electricity is the movement of these electrons through the wire. Resistance is caused when the free electrons moving through the wire collide with the atoms making their path through the wire more difficult. This means that if there are more atoms in the way to collide with the free electrons the resistance is increased. In a length of wire there will be a number of atoms, and in a wire twice the length, there will be twice the number of atoms. In turn this will lead to there being double the number of collisions between the electrons and the atoms increasing the resistance by 2. This explains why the results were directly proportional. For example a wire that was 10 cm long may have 500 atoms blocking the electrons. Therefore in a wire 20 cm long, there would be 1000 atoms meaning that the resistance had doubled.
The results that I have obtained support my original prediction. This is because in the prediction I said that as the wire length increased, the resistance should increase. The results have shown that this is true.
The line of best fit clearly shows that the results followed the expected pattern very well, although I had one result which was slightly further away form the line to the others, this may have been because I read the meter wrong, or I did not have the length exactly correct. The rest of the points are very close if not touching the line. This shows how the results were directly proportional through out, as the gradient remained the same.
I could improve the reliability of this investigation by:
- Repeating the experiment again
- Doing the experiment again but with a different thickness of wire
- Changing the current to maybe 0.30Ohms or 0.40Ohms, to see if it makes a difference to the theory that when the length increases, so does the resistance
- Use a larger range of length, maybe going up to 200cm and seeing whether the resistance will still be proportional to the length
In conclusion, I feel my results were fairly reliable, as it proved my prediction and the theory of length been proportional to resistance.
