Trial Investigation: we set up the circuit and these were my results.
During this trial run I have found many ways to improve the experiment so that it is fair and gives me better more accurate results.
- I noticed that the voltage changed each time we changed the lengths, so to make it fair I will use a variable resistor in my investigation. This will allow me to adjust the voltage to 1.
- I will also use sellotape to make sure the wire stay straight along the wire so that the length is correct.
- I also think that the range of lengths I used was not wide enough so I will measure the wire up to the length of 55cm and measure at 5cm intervals.
Prediction: I predict that the longer the wire the more resistance because as the length of the wire increases the number of collisions increase causing the resistance to increase. This will happen because by increasing the length of the wire, will increase the amount of electrons in the wire, these will collide with the atoms so therefore increasing the resistance.
Method:
- Get all the equipment needed :
- 4 crocodile clips;
- 4 normal wires;
- An ammeter;
- A variable resistor;
- A multimeter/ voltmeter;
- Michrome wire – gauge 32, diameter 0.28mm;
- Meter rule;
- Power pack;
- Sellotape.
- Set up the circuit:
The ammeter must be connected to the resistor and the wire, the multimeter to both ends of the wire and the resistor to the ammeter and the wire.
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Then I made sure the clips were clipped on the 0 and the 1st length of the wire (5cm).
- Then I made sure I set the multimeter to 20.
- After that I switched on the power pack and moved the resistor to make the voltage 1.
- I then took the current reading as quickly as I could and switched off the power pack. I had to keep switching the power pack of after every reading so that the wire did not get too hot and affect the experiment.
- Then I moved the crocodile clip along to increase the length by 5cm.
- I then repeated steps 5-7 for all the different lengths.
- After this I repeated the experiment 2 more times.
- As I was going along I wrote down all of the results and then took an average of the 3 runs. I did this by adding them all together and the dividing the answer by 3. Then using the average current I found the resistance by using the formula R=V
I
The lengths I used were from 5cm to 55cm and I measured the wire in 5cm intervals.
I made the experiment a fair test by:
- Using the same wire all the way through;
- Switching off the power pack as soon as the reading was taken;
- I kept the diameter of the wire the same;
- I changed the lengths in the same amount of centimetres each time.
Results:
Analysis: I have plotted my results on a graph, then I drew a line of best fit on it and found the gradient from the line. To find the gradient I used the formula gradient = resistance.
Length
The gradient of my graph was 2 which gave me the answer 0.2 Ω/cm
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My results show me that my prediction was correct. It tells me that as the length of the wire increases the amount of resistance increases. I can tell this because my graph shows strong negative correlation as most of the points follow the line of best fit and the points that don’t are very close to the line. This shows me that there is a pattern between resistance and length of a wire. It tells me that as the positive ions gain kinetic energy from the electrons during collisions, which leads to the frequency of the collisions to increase. This is the heating effect of the current and causes the resistance to increase.
My gradient tells me that there is 0.2Ω of resistance per centimetre of the wire. In my prediction I said that the resistance will increase as the length of the wire increases, and I said it would do this because there will be more collisions in the wire as the length increases so it will create more resistance. My experiment has proved my prediction right because my results show a steady increase in the resistance as the length increase and the correlation is strong. The gradient of my graph provides firm evidence about the effect of length on electrical resistance.
Evaluation:
Accuracy: I made sure that my experiment was as accurate as possible
- I made sure the wire was straight so that the length was accurate;
- I measured the lengths in centimetres and it was clear to measure it against the ruler so it was accurate;
- The equipment I used was accurate as my results show a clear link between length and resistance in a wire, the results may have been more accurate if the had been plotted to 2 or 3 decimal places but it still would have been the same strong negative correlation;
- When I took the readings I made sure that the current wasn’t flowing around the circuit for too long so that the wire did not get heated up and affect the experiment, by turning the power pack of straight after taking the reading. If I had left it on the ‘heating effect of the current’ would have happened and then the resistances would have increased and the current value would have decreased.
Reliability: I did a few things to make sure my results were reliable:
- I repeated the results three times and the found and average o the results and used it to find the resistance;
- I used a wide range of lengths and took the readings at equal intervals of 5cms. This seemed to have been a good range a it has given me conclusive results with a definite pattern.
Improvements: if I were to do this experiment again the improvements I would make are:
- That I consider the resistance in the rest of the circuit, because the length of the copper leads may have affected the total resistance of the circuit;
- I could expand the experiment by using more lengths of the wire;
- I could also use my gradient of my graph to calculate the amount of resistance per length of wire.
I could also expand the investigation by repeating the experiment but using different materials, so I could use a different material of wire and change the lengths – I think that the resistance will be different to other materials because they all have different atomic structures, so they will have different conductivities. But I would expect the resistance to increase steadily with the length of the wire increasing. I could also just use the same material but just increase the thickness of the wire and then change the lengths and see how thicker wires affects resistance. If I were to do this I would expect a low range of results for resistance for a larger diameter of wire. I will expect this because more current will flow through the wire and there will be less resistance, but this will only happen if I allow the same voltage to flow through the wires in both experiments.
