Safety Considerations,
I will make sure I am wearing safety goggles at all time to prevent the wire damaging my eyes.
I will keep the voltage passed through my wire below 3 Volts so the wire does not heat up.
Lengths of below 10cm will not be experimented on to prevent overheating.
Intended readings,
The longer the wire the larger the resistance should be. This will make the resistance smaller.
Constantan,
Design Justifications,
I chose to stay below 3Volts because when I tested how many volts needed to heat up the constantan wire it was just over 3Volts, so if I stay below 3Volts then there should be no problems with temperature change in the wire.
The experiment I carried out to find the temperature change was by wrapping a section of the constantan wire around the bottom of a thermometer. I then sent a current through the wire and took note of when the temperature started to rise.
This was at 0.33A.
I found the radius of the wire by using a micrometer to read the diameter then divided the reading i got by two.
To find the length of the wire i used a meter rule, which was taped to the side of the wire.
I found the cross-sectional area of the wire by using the radius that i found and squaring it then multiplying it by pie.
Then using the area i found the length/area which was =L
A
Then to get the same amount of amps i set the ammeter to 0.25A at the beginning of every experiment.
To get the volts i read the voltage of the voltmeter when the current was set.
To get the average Volts i added all the different attempts together then divided them by the amount of them. Which were three attempts.
To find the resistance i used the formula P=V
I
To find the resistivity i used this formula,
Resistance = V Cross sectional area = r²
I
Resistivity = resistance x cross sectional area
Length
P = V x r²
I
L
Report,
My aim is to measure the resistivity of the wire alloy “Constantan”
Possible Sources of errors,
Errors could have occurred because the wire along the meter rule was not straight as it might have been. It had a few bends in it, which may have altered the length. With this in mind the different lengths will not be accurate when attaching the crocodile clips in the relevant places.
Other possible sources of errors could have been the tools, which I used. They say, “You are only as good as the tools you use”
Which is right, because if there was a fault with any of the, micrometer, Voltmeter or Ammeter then this experiment will be inaccurate.
Minimising the errors,
Errors were minimised by repeating the experiment three times to make any outstanding results known. Also I stretched the wire as much as I could to try and straighten the wire out but it still had curves in it.
The most significant measurement,
P=I x A P=I x r²
V V
L L
If the radius is incorrect, then you will be squaring an incorrect answer, which will then determine the resistivity. The radius will have the largest effect on the final resistivity if incorrect.
Numerical analysis of the data,
The gradient of the is 4.50x10 which is the resistivity. I believe that this is a correct value for Constantan because from my tables the resistivity was 5.26x10 so the power of ten is correct. Considering there may have been errors then this is a close enough answer.
From my graph I cannot spot any drastic outliers, which will have messed up my experiment. This shows that my experiment was carried out successfully and has worked well.
The only result which I got which may be called an semi anomalous result would be the one which I have labelled on my graph. I believe this is a slight deviation from the line of best fit more than the others. This was not much of a change so there was no drastic change.
Qualitative analysis of the data,
There was only one anomalous result because it is the only one, which stands out from the graph more than the others.
To find the gradient of the line of best fit on my graph, I drew a triangle were the gradient was the hypotenuse.
I made the sides of my triangle 18cm by 9cm just to make than bigger than 8cm by 8cm so that it worked sufficiently.
Modifications,
What I set out to do and what I actually did were more or less exactly the same. The difference was that after taking the readings I left the circuit for 30 seconds to ensure the wire does not heat up just even a little bit, because this would alter the readings and mess up the results.
Evaluation,
My final result,
Is that there were two results i have derived for the resistivity of constantan alloy, which are,
5.26x10
4.50x10
Were both good values and were good because I had to put up with possible errors.
Reliability,
The reliability of the techniques i used was good for this experiment. I believe the results would have been more accurate using more accurate and expensive equipment.
The only way to make my experiment more reliable would be to do it again and again. This will make it more accurate.
Improvements,
With taking the possible errors in to account,
If i were to improve this experiment i would probably do the experiment with different pieces of constantan wire to make sure that the wire i was using for the experiment was not faulty.
When doing the experiment in the future I would repeat the experiment over a lot more times to get a better average to use for each variable, and a lot more accurate results.
I would try to make sure I don’t get any anomalous results which would make my experiment just that little bit more accurate.
