Prediction
We know that resistance is proportional to the length of a wire using the formula:
Resistance = Resistivity X Length
Cross sectional Area
I predict that if the length increases then the resistance will also increase. I think this because the longer the wire the more atoms the electrons will collide with. From this I also think that the resistance will increase in direct proportion to the length of the wire, so if the length is doubled, so will the resistance. This is because if the length is doubled so will the number of atoms in the wire, resulting in twice the number of collisions in the wire. My graph should show the length is directly proportional to the resistance.
Trial Experiment – In this experiment I will choose the thickness if wire that I want to use in my main experiment. To do this I will test different wires with different thickness’. To ensure a fair test whilst carrying out the trial experiment I will only change one independent variable, the thickness. I will then work out the resistance for each thickness, at two different lengths
The wire that I consider to have the best results will be the one I use for my main experiment. Here is the circuit diagram for the trial experiment;
Results from the Trial.
Looking at these results I decided to use the wire with thickness 28. I have chosen this thickness because it is in the middle of the thickness’ tested and the resistance data it gave was manageable.
I worked out the resistance by taking the reading off the voltmeter and the ammeter, and using the formula;
Resistance = Voltage R = V
Current I
This is OHMS law, stating that resistance is voltage divided by current.
Improvements I could make from the trial experiment are that I will record the volts and amps in my results table as well to make sure there are no calculation errors. I will also test longer pieces of wire.
Method
Apparatus:
Power Supply
Ammeter
Voltmeter
28 Constantin Wire
Meter Ruler
Crocodile clips
Connecting wires
I have chosen 28 constantin wire as from my trial results I found it the most accurate type of wire, and manageable.
To collect the data for my graph I have chosen to take a range of 8 lengths, this will ensure a large range for the graph, and should make it more accurate. I have also chosen to repeat each length three times and then take an average, I have chosen to do this so that if there are any anomalous results then they should not show when I plot the averages on the graph. The lengths I have chosen are: 10cm, 20cm, 30cm, 40cm, 50cm, 60cm, 70cm and 80cm, These lengths give a good range.
Below is a circuit diagram of my main experiment, I haven’t changed the circuit I used for my trail because it was very effective, and I didn’t see any need too.
Results
From this graph I can see that the resistance of the wire is directly proportional to the length of the wire. I know this because the Line of Best fit is a straight line showing that if the length of the wire is increased then the resistance of the wire will also increase.
Conclusion
In my prediction I said that;
“I predict that if the length increases then the resistance will also increase…
My graph should show the length is directly proportional to the resistance.”
From my graph I have shown that my prediction was correct, as the line of best fit is a straight line proving that the resistance of the wire is proportional to the length of wire. The length of wire affects the resistance of wire because the number of atoms in the wire increases or decreases in proportion to the length.
The resistance of a wire depends on the number of collisions the electrons have with the atoms of the material, so if there is a large number of atoms there will be a larger number of collisions, which will increase the resistance of the wire. If a length of a wire contains a certain number of atoms when that length is increased, so will the number of atoms.
Also if the length of the wire was doubled or tripled then the resistance would also double or triple, this is why it is directly proportional.
Evaluation
From my results table and graph I can see that although my results gave a good trend of the results, they were not perfectly accurate, not lying exactly on the line of best fit. Though there weren’t any anomalies that stood out.
Some of the result may not have laid exactly on the line because of inaccurate equipment, human error or faults in the experiment.
During the experiment I noticed several modifications I could make to improve the investigation. To be more accurate in my investigation I would instead of using crocodile clips to connect the wire, use pointers. This would be more accurate because the tips would have a much smaller surface area than the crocodile clips, giving a more accurate measurement of the length of wire.
Also if there were a way of preventing the wire being tested heating up I would do this as if the wire gets hot, then the resistance is affected. It is affected due to the atoms having more energy and moving faster, causing more collisions.
As well as these modifications to expand on my investigation I would investigate other factors that affect the resistance of a wire, such as width and material.