Throughout this experiment the potential difference should stay the same. This factor affects resistance so if this factor is not kept the same the results will not be accurate. The last controllable thing that should be kept the same is the length of the wire(s) as this will also increase resistance.
There is one factor that will not be able to be kept the same, which is temperature. This we be the main problem of this experiment. The problem is that the greater the temperature the greater the resistance. The only way to overcome this problem(with the equipment available) is to simply leave the circuit switched on for the smallest possible time.
The aim of this experiment is to find the relationship between x-sectional area and resistance, the first part required to achieve this is to measure the X-sectional area of the wire (covered earlier in the method). The second part is finding the resistance of the circuit. To unmask this the formula R=V/I must be used. To use this the potential difference has to be found along with the current. As mentioned earlier these can be found using a voltmeter and an ammeter.
The only real safety measurement taken is to use a low voltage to prevent wires heating up and burning.
The measurements taken and how I will take them are as follows: -
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the x-sectional area of the wire: -micrometer to find diameter, divide diameter by 2 to find radius and use ∏r2
- the potential difference: -voltmeter
- the current: -ammeter
- the length of the wire: -ruler
- the resistance: - R=V/I, resistance=p.d/current
Prediction
I think that as the x-sectional area is doubled the resistance is halved. My prediction is largely generated by the rule of resistivity (R=ρl/A), resistance is inversely proportional to the x-sectional area of the wire. what this basically means is if the x-sectional area is doubled the resistance is halved. This is because of the fact that as the area increases so does the current; this means there is more room for the electrons to get through the wire. This brings upon an increase in the current, which will cause a decrease in resistance. Unfortunately we are unable to mesure the resistance of just the wires we are also including the resistance of every other part of the circuit, e.g. Power pack, copper wires etc.
Results
My results show that resistance decreases as the area increases. The science behind this is the R=ρl/A rule. We know the R (resistance) will decrease simply from knowing that A (area) increases. The real reason for the resistance decreasing is that electrons move more freely (I=Q/T). I used the formula ∏r2 to find the area of the nicrome wire. I firstly found the diameter of the wire using the micrometer(0.28mm) then I divided the diameter by two, finding the radius(0.14mm)and finally I multiplied the radius by ∏2(0.06mm2).
Analysis
My results clearly show that as area increases resistance decreases. There was a fairly large range in my results for this experiment, I recorded a lowest of 2.1Ω and a highest of 8.9Ω. I soon realised that the rule R=ρl/A could not be used to an accurate extent here, mainly due to the fact of resistance from all the other parts to the circuit. Instead of just getting the readings for the resistance in the nicrome wire I got the resistance for the whole of my circuit. Although I did not get the correct results from the R=ρl/A rule my prediction was still correct in the fact that I predicted the resistance would decrease as the area increased.
Evaluation
When undertaking my experiment I did not really come across any large problems. The biggest problem for me was my ammeter broke half way through the experiment so I had to restart it so there would not be a huge impact on my results. One other problem was the wire(s) heating up (thus increasing the resistance). The last problem I faced was even with the new ammeter was it gave different results even though all factors remained the same, length of wire, voltage etc.
If I had the chance to retry this experiment I would try to conquer the problems I faced in different ways. I would conquer the broken ammeter problem with a newer more reliable ammeter. The next problem of the wires heating up, this I would tackle with some sort of cooling system like a fan.
I trust my evidence to be good and reliable, as I did not record any anomalous results. I am quite please for my results to have almost matched my prediction using the rule R=ρl/A.