In the experiment, the variables apart from the length will be kept the same to make a fair test.
If the experiment was done in perfect conditions, the results would look like this;
(Taken from “Physics matters” text book)
We can see from the above results that if you double the length of the wire, you double the resistance. This pattern will only exist if all of the factors are kept the same.
To make the experiment safe I will –
- Keep the voltage to the value of 3.00 V
- Only let the current run for as long as it takes to write down a reading (these two points will reduce the heat produced in the wire and so reduce the risk of burns)
- Wear eye protection (incase of the wire fusing and throwing small pieces of wire into the air)
Prediction
I predict that the wire will resist more as the length is increased. I predict this because it is a fact that the resistance will increase as the resistor increases in size, because there is more atoms that the current has to pass through. The other factor that may affect the resistance is the temperature of the wire. I also predict that the finished line graph will slightly straighten out at the end because the temperature will increase as the voltage passes through.
Equipment
The equipment used for this experiment was:
- 100cm piece of wire
- Power pack
- Voltmeter
- Ammeter
- Wires
- Crocodile clips
- Meter rule
Method
The power pack must be set up with the wires leading out of it and set to 4v. Connect the wire to an ammeter and then to a resistor by crocodile clips. Place the voltmeter and the resistor parallel to see the potential difference across the wire. Then the wires need to be joined into a variable resistor to keep the voltage at 3.00 V and into the power pack.
Like this:
I started at 200 mm and turned the power pack on, moved the variable resistor so that the voltage was at 3.00 V, took the readings down and turned the power pack off, to stop the wire heating up, and resized the length of the wire to 300mm against the meter rule. Then turn the power pack back on and take down the readings, turn off the power pack, and move the crocodile clip another 100mm, continue this until you get to 800mm at least. Do the experiment 3 times to get an average to get more accurate results.
The variables in this experiment are the length of the wire and the thickness of the wire.
I made this experiment a fair test by keeping the voltage the same every time I measured a reading, using the same wire so that the diameter and material of the resistor were the same. This would have kept the experiment a fair test as there was no advantage or disadvantage for each experiment that was taken.
Results
1st set of results
2nd set of results
3rd set of results
Average set of results
Analysis
Using scientific knowledge, my graphs have turned out as they should have and my results are accurate. As the length of the wire increases, the voltage increases but the current decreases.
Using the equation;
Resistance = Voltage / Current I have worked out the resistance, according to Ohm’s Law.
From my graph, I have found the pattern that the higher the voltage, the higher the resistance becomes. The graph shows that as the length of the wire increases, so does the resistance of the wire. An example of this is when the experiment at 400 mm was taken place and the resistance was 2.36. When 100 mm more were added on, the amount of resistance at 500 mm was 1.86. This is because the current passes through more atoms in the wire and creating more resistance for the current.
I could not find any pattern in my results, but the graph still looks correct. At the end, the line slightly straightens out, this was expected as there was heat generated and the atoms would have been moving more, causing more resistance. The obvious outcome in the results was that the longer the wire, the more resistance there is due to the current having to pass through more atoms. My results support my prediction and research because I predicted that the graph would straighten slightly at the end. I also predicted that the longer the wire, the more resistance. With the 3 repeated experiments, the difference (if any) between each one is very small. Everything has happened in this experiment as I had expected.
Evaluation
In this experiment, the errors that could have occurred were: -
- The length of the wire was not very accurate, as we could have measured the wire a few millimeters off, which could have affected the whole experiment.
- The value of the ammeter and voltmeter could have varied, meaning people may have written down different results. This would affect the experiment because people would have written down a higher or lower result for the voltmeter and the ammeter so that the worked out resistance is possibly higher or lower.
- The power pack might have not been turned off during the change of length of the wire so heat would build up, causing more resistance on the next experiment of the increased or decreased wire length.
If I were to make improvements on the experiment, I would have tried to make the wire lengths as accurate as possible, although in this experiment there were no extremely odd results.
An experiment that I could have done to make sure that the experiment fairer would have been to keep the resistor under a constant temperature. The circuit would be the same, but the resistor would be under a temperature so that the resistivity of the wire was kept the same. Possibly under water the temperature would have been the same.
The reason this would make the experiment fairer would be because there would be no slant at the end of the graph. Without a constant temperature, there is more resistance if the temperature rises, because to atoms with kinetic energy.
I have made my experiment accurate, by turning the power pack off while changing the length of the resistor, to stop the resistor heating up and causing more resistance.
I have made my experiment reliable, by doing the experiment several times, and averaging my results emitting any anomalies.
For my conclusion, I have found out that the resistance and the voltage are the same if the current is kept the same and that the resistance and the voltage are in proportion with the length of the wire.
Jack Cummins 10LB
