R=V/I resistance= voltage/current
Resistivity: p=RA/l
Resistivity=resistance X cross section of the wire / length of wire
PRELIMINARY REULTS
We did a short preliminary experiment to see how the resistance affected the temperature of the wire, when we put one crocodile clip at 0mm and one at 100mm the wire got so hot it began to burn and give off smoke. From this preliminary experiment we decided not to take any measurements under 100mm because it could become unsafe.
RANGE OF RESULTS
We have decided to take results at 100mm, 200mm, 300mm, 400mm, 500mm, 600mm, 700mm, 800mm and 900mm we shall take each measurement twice. This should give us a wide enough range of results to plot on Graphs we will also re-do any anomalous results
PREDICTION
I predict that as the length increases so will the Resistance because Ohms law states that potential difference is directly proportional to current and the current will increase as the length of the wire increases because there will be more resistance on it (it will be more spread out, current is carried by electrons in metals)
SAFE TEST
To make sure everything is safe whilst carrying out the experiment safety goggles must be worn and the wire must not be touched while current is flowing round it and shortly after because it will be hot.
FAIR TEST
To make sure the investigation is fair, we will use the same equipment each time, monitor the temperature (if the wire start to give off smoke we will stop and give it time to cool down to reduce anomalies) and we will measure our wire using a micrometer to check the width before doing any equations.
EQUIPEMENT
Power pack, to power our experiment so current flows through the wire.
Ammeter, to measure the current flowing round our circuit.
Voltmeter, to measure the voltage of our circuit.
1m Nicrome Wire, to test.
Wire, to put, our circuit together with.
Metre rule, to measure the lengths of wires.
Crocodile clips, to hold wires in place.
DIAGRAM
METHOD
- set up apparatus as above
- Put crocodile clips at 0mm and 900mm
- Turn power pack on
- record Current and Volts
- Turn off Power pack
- Repeat steps 1-4
- Repeat steps 2-6 but with 800mm.700mm, 600mm,500mm,400mm,300mm,200mm and 100mm
We can clearly see my results are correct because the constant is constant. To make our results accurate we used the same equipment each time, kept an eye on the temperature(When the wire started to give off smoke we stopped and give it time to cool down to reduce anomalies), we used digital a digital ammeter and voltmeter to reduce human error and we measured our wire using a micrometer to check the width before doing any equations. The width was 26mgs which is : 0.45 mm.
ANAYLSIS
We can clearly se that our graph supports our prediction, As the length increases so does the resistance, this tells us that Length and resistance are directly proportional.
We can now work out the resistivity of the different lengths of wire:
100mm
Resistivity=0.785 x 0.45
100
Resistivity=0.00353
200mm
Resistivity=1.49 x 0.45
200
Resistivity= 0.00335
300mm
Resistivity=2.11 x 0.45
300
Resistivity= 0.00352
400mm
Resistivity=1.34 x 0.45
400
Resistivity= 0.00151
500mm
Resistivity= 1.055 x 0.45
500
Resistivity= 0.00095
600mm
Resistivity= 0.88 x 0.45
600
Resistivity= 0.00066
700mm
Resistivity=0.81 x 0.45
700
Resistivity= 0.00052
800mm
Resistivity=0.71 x 0.45
800
Resistivity=0.00040
900mm
Resistivity= 0.62 x 0.45
900
Resistivity= 0.00031
EVALUATION
Only one anomalous result was obvious whilst carrying out our investigation (at 700mm) so we went back and did it again. Unfortunately when looking at my graph it seems there were more anomalies, I have circled them in the table and on the graph. I think the anomalies may have occurred because our battery pack broke and we had to get a replacement. Apart from the battery pack everything else went safely and well. Our preliminary experiments allowed us to make sure the wire did not get too hot which meant we did not get any anomalies around 100mm and that we were safer. I think our range was big enough but if we had more time I would have liked to done another repeat and possibly take measurements at 50mm intervals to achieve a greater range of results. I thought our results were really good they clearly supported our prediction that as length increases so does resistance. If I was to further this experiment I would use different metals and see which had the best resistivity, I would not use a metre rule because it was easy for human error to occur as it was not particularly detailed perhaps a digital measuring device would have been better. I might also try a different variable such as diameter of wire to see how that affected the resistance. Overall I was very pleased with our investigation and think that we did all we could to do it well.
