Apparatus:
This experiment will need a lot of equipment. This will include the connecting wires, for connecting, two crocodile clips, to attach to the wire at different measurements, a one meter long bare wire to measure the variation in the resistance concerning the length used. The wire will have to have 30 SWG (standard wire gauge) with a diameter of 32mm. A voltmeter to measure the voltage, an ammeter to measure the current across the circuit, a meter ruler to measure the length of the wire, a power pack to give the direct current for the circuit.
Accuracy:
We will make sure the measurements are accurate by checking each result as we take it down. We will take each recording twice to make sure each measurement is not anomalous. Then we will work out the mean of each to make the results more accurate. Repeat measurements will show out any irregular measurements.
Fair Test:
To keep our experiment a fair test, we will need to keep some of the variables unchanged. The only variable we will be changing is the length of the wire. We will be not changing the thickness of wire as it can affect the resistance, where as so will the type of metal used. We will keep the power pack at 4 volts to make sure the wire does not become damaged in any way, which may later affect the readings. Making this a fair test will ensure the accuracy of our readings.
Safety:
We will make sure we are safe by wearing gloves so the hot wire does not burn us. We will use 4 volts for our experiment so we do not overheat our experiment and make sure that we are safe. We will keep any long hair tied back just for extra safety. We will only turn on the power supply when we are using the electricity for our circuit. We will not misuse any equipment. We will not measure the resistance of a wire with a measurement below 10cm, as it would cause the wire to get hot and may even cause the wire to burn.
Method:
- At first we will be collecting all the equipment needed for this experiment, a metre bare wire, 5 connecting wires, a voltmeter, an ammeter, two crocodile clips, a metre ruler and a power pack.
- We will then put the circuit together.
- We will then connect the crocodile clips to 0cm and 5cm.
- Then we will set the power pack voltage to 4 volts and switch it on.
- We will then take down the results and move the crocodile clip placed at 5cm to 10cm. After each measurements reading has been taken down, we will move the clip on 5cm further. You do this until you have taken all the readings. There is always one at this end, whereas the other one keeps moving along.
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After taking down the readings we will then work out the resistance.
This will be worked out using Ohm’s law
- We will then repeat the experiment to make our results more accurate.
- We will take down our readings in two tables.
- A graph will be drawn to show our results.
Results:
First set of results
Second set of results
Observations:
When we were doing our experiment we saw made some observations. We saw that when we started our experiment by measuring the readings of a 10cm bare wire, the wire was hot as it was glowing, but not too much. We also noticed that the voltmeter never showed a constant figure. The integers kept changing, where as the ammeter stayed constant
Resistivity:
The resistivity is worked out by using the equation R= ρl
A
L= length of bare wire
A= area of wire
ρ= resistivity
R= resistance
In my experiment we worked out the resistivity for the 50cm bare wire
L= 50
A= π(162)= 8.042cm2
R= 7.66
ρ= 1.232
The resistivity is 1.232
Conclusion:
Our results were very similar to each other as we took them twice to ensure accuracy. The line of best fit for our graph was a straight line giving the idea that the resistance is proportional to the length of bare wire. This tells us that the longer the length of bare wire, the more the resistance.
My prediction was right in the way that the resistance is proportional to the length of wire, though it does not double as I predicted it would. It supports Ohms law as he said, “current through ∝ voltage across the wire providing the temperature remains constant”
The gradient of the graph is 1/3. It has a strong positive correlation, which shows the relationship between the resistance and the length of the wire.
Evaluation:
There were many ways that we could have improved the experiment. We could have used a straight piece of wire; this affects the experiment because this varies the length of the wire by making it longer. We could have changed the wire every time we used it to make to ensure that if the wire got damaged it wouldn’t affect the wire resistance in any way.
We might have made it inaccurate by using a wire, which was not visibly straight; this may have caused error in measuring the wire perfectly. The wire had cello tape attached to it to keep it stuck to the ruler so we could measure the length of the wire more easily. This might have made it inaccurate as the cello could have an affect on the circuit, as it is part of it.
My points were very close to the line of best fit. This indicates that our results were reliable and that we did not have any anomalous results. Our experiment was accurate and our results had a very strong correlation. My points were practically along the straight line signifying we did not make mistakes during taking results and it was a fair test.
The diameter of the wire was measured by an engineering piece of equipment. This was tightened around the wire and then when we couldn’t tighten it any more, we read the measurement. It gave us the measurement of 32mm.
We realised that when length of wire = 0 there was still resistance. This is because the connecting wires are the wires causing the resistance. In any circuit there will always be resistance.
