The diagram on the next page will show this more clearly:
½ of length of wire
+ E + + + E + E +
+ E + E + + + E
Double the length of the wire
+ + E + + + + E + + + E
+ + E + + + + E + + + E +
The diagram above shows us clearly that when the length of the wire is doubled there is more chance of free electrons bumping into fixed atoms. This will mean that the resistance will increase because the electrons will loose more of its charge/energy as heat.
Apparatus
For this experiment the following equipment would need to be used:
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Power pack – To apply voltage through out the circuit.
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Meter Rule – To measure how long the wire is and to give the wire a base.
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Wire – We will be measuring the resistance of this.
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Voltmeter – This will be connected in parallel with the wire to measure its voltage.
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Ammeter – This will be connected in series and will be used to measure the current in the circuit.
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Crocodile clips – To connect the different parts of the circuit together.
Diagram
Meter rule
Wire
Crocodile clips
Method
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Set up apparatus as shown in diagram above.
- Put the power pack on 4 volts.
- Start taking results when the length of the wire is 20 cm.
- Take results of current and voltage.
- Increase length of wire by 20 cm.
- Repeat 4 & 5 until wire is 1m long.
- Repeat experiment 3 times to get perfect results and then calculate the resistance.
Safety
To keep the experiment safe make sure whilst connecting up equipment the power is off.
Make sure the power pack is not more than 4 volts.
Do not touch the hot wire or you may burn your hand.
Make sure you do not have wet hands or that water is not near your experiment.
Fair Testing
To make the experiment fair I will keep the power pack on 4 volts through out the test.
I will keep the thickness of the wire the same through out the experiment.
I will keep the type of the wire the same through out the experiment.
I will note down the exact results on the ammeter and voltmeter.
I will follow the method correctly.
Results
Preliminary results
Before my experiment to help me I did some preliminary results, this was to help me with my real experiment. By doing these preliminary results it enabled me to get some sort of idea about doing the experiment I am doing and what kind of results I should get from it. This helped me in writing up this plan.
On page 4 there is a graph of my results:
.
OBSERVATIONS
From my experiments these are the results I collected:
1st set of results
2nd set of results
3rd set of results
Average results
Whilst collecting my results I made sure that the crocodile clips were securely attaching each part of the circuit together.
I also made sure that the power pack was on 4 volts. I made sure the voltmeter was connected to the metal wire in parallel and the ammeter was connected to the circuit in series. This enabled me to get more accurate results.
Also, I believe my results are accurate because I repeated the experiment three times and averaged my results to get near perfect results.
Also as there are no anonymous points in my graph it means that I have not made a mistake whilst doing the experiment. Therefore there is even more chance of my results being accurate.
On the next page there is a graph of my average results:
ANALYSIS
From my average results and the graph, in my observation, I can see that as the length of the wire increased so did its resistance. I know this because the graph has a positive correlation and a line of best fit, which is a straight-line, meaning that the length of the wire is proportional to its resistance.
This graph has a pattern. The graph’s pattern is that as the length of the wire increases, the resistance also increases. This is because using ‘Ohms Law’ we know that as the distance between the ends of the conductor increases, then the resistance will increase. Therefore using this I know that when the length of the conductor is at its smallest its resistance will also be at its smallest.
This pattern is also shown on the graph because when the length of the wire is at it’s smallest (20cm), then the resistance is also at its lowest (0.57 Ohms). Also on the graph it is shown that as the length of the wire gradually increases, the resistance is also increasing in proportion to it and when the wire is at its longest (100cm) the resistance is also at it’s highest (2.91 Ohms).
CONCLUSION
In conclusion, it can be seen that when the length of the wire increases so does its resistance. This means that my prediction is true because using my graph it has been proven that as the length of the wire increases so will its resistance. This is because as the wire length increases, it will mean that free electrons will have to travel further than they needed to before in the wire. Therefore the free electrons will loose some of their charge as heat. As a result of this the current decreased, therefore making the resistance in the wire increase. This happened because, when the wire length was long there were more fixed atoms and impurities in the metal wire, which meant that more free electrons collided with the atoms and impurities and other free electrons, which meant that more energy was lost, therefore the resistance of the metal wire increased. So, when the length of the wire was at its longest the amount of fixed atoms and impurities in the metal wire increased, which meant that there was more chance of free electrons colliding into them. This caused more energy to be lost in the form of heat, which meant that the resistance of the wire further increased.
EVALUATION
My experiment worked well. I managed to set up my equipment and collect my results without having any problems.
To make my results accurate I made sure that the circuit was all attached properly and securely using crocodile clips. I made sure that the power pack was on 4 volts through out taking my results. I made sure the voltmeter was connected to the metal wire in parallel and the ammeter was connected to the circuit in series.
Also, I believe my results are accurate because I repeated the experiment three times and averaged my results to get near perfect results. Another reason why I think my results are accurate is because there are no anonymous points in my graph which means that I have not made a mistake whilst doing the experiment.
Although having said this I feel that I could have made my results even more accurate. I could have done this by noting down the resistance each time after increasing the length of the wire by 10cm instead of noting down the resistance after increasing the wire by 20cm each time.
However, my results are reliable because I made sure that my experiment was fair. I did this by keeping the power pack on 4 volts through out the experiment, by keeping the thickness of the wire the same through out the experiment, by keeping the type of the wire the same through out the experiment, by noting down the exact results on the ammeter and voltmeter and by following the method correctly.
My results are also reliable because they followed the scientific theory of ‘as the distance between the ends of the conductor increases, the resistance will also increase.’ This is shown on my graph in the observations.
Some additional work could have been done in this experiment. I could have seen how the resistance of the wire is affected by the other key factors, which were mentioned in my plan. For example the thickness of the wire and the type of the wire.
Overall, I feel my experiment worked well and was a success.