Metals conduct electricity because the electrons in the metal can move about more. The reason why wires give lots of different resistance’s is down to the number of free electrons in the metal- these free electrons aren’t involved in bonding, in a pure metal conductor. If you increase the voltage across a component, more current will flow through it.
Hypothesis
I think that when the length of wire under test is increased the resistance of the wire will increase if the thickness, type of wire and current are kept the same. This is because the longer the wire, the more times the free electrons will collide with other electrons and any impurities in the metal. Therefore, more energy is going to be lost in these collisions (as heat).
I also think that if I double the length of the wire its resistance will also double.
Predicted graph: -
Apparatus
Power pack, variable resistor, 6 connecting wires, Ammeter, Voltmeter, Wire under test and 2 crocodile clips.
Diagram
Method
- Set up apparatus as in diagram.
- Also make sure that on the dial the voltmeter is set to 20V, that on the dial the ammeter is set to 20A and that the connections are right.
- Set the ammeter to show 0.2 on the display by moving the dial on the power pack, this will stay the same throughout the experiments.
- Make sure to switch on the power pack at the mains after wiring up.
- Move the crocodile clip along the wire going up in 10’s, the range is 0-100cm.
- Read the amount of volts measured off the voltmeter at each of these intervals.
- Record all results.
- Once all results have been collected work out the resistance, which is volts/amps.
- Then repeat the experiment for reliability.
- Work out an average resistance of the 2 sets of results.
- Draw a graph of the average results.
- I didn’t have any unreliable results but if any results were taken that seemed wrong compared to the others, that length should be repeated as well to check its reliability.
Safety
In order to perform a safe experiment I decided to keep the voltage lower than 1V so that no over heating will occur.
Results
Experiment no.1
Experiment no.2
Average Resistance (Ω)
Graph of average resistance
Conclusion
I have found out that when the length of the wire under test is increased the resistance of the wire will increase if all other aspects of the experiment were kept the same. This is was my prediction said, and so this experiment proves it is correct. I was corrects because as you can see the longer the wire the higher the resistance. Resistance is caused by the difficulty of electrons moving atom to atom down the wire. It is hard for the free electrons in the outer shell to pass from atom to atom because the wire has a large resistance. A long wire has more electrical resistance so each electron has more atoms to hop along. The heating effect occurs as each electron hops along the wire.
In the graph there is a positive correlation because the higher the resistance the longer the length of wire. The line of best fit could not be done because all of the points were in a straight line, which shows that the experiment was performed well and that the results are reliable.
It also shows as in my prediction that if I doubled the length that the resistance would also double.
Evaluation
I found the procedure that I used easy to do and it went very well. It also produced the results that I expected. My results were very accurate. Which is shown in the graph, as they are all in a straight line with no anomalous results.
I feel that the experiment was suitable and a good experiment to do. I got out of the experiment what I had expected to.
I think that the only way that I could improve my results are either by doing more experiments for increased reliability, by repeating the experiment with a different wire to confirm my results or by doing a new experiment, by changing thickness and then seeing what the differences there were between the two experiments.
While doing the experiment I knew that the wire would heat up and so it would not be a fair test, so I turned off the power supply between readings so that the test was fair.
