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Investigating (one of) the factors that affect resistance.

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Caroline Morris        Physics Coursework        

Investigating (one of) the factors that affect resistance

Resistance is the property of an electrical conductor, to work against the flow of the current and change some of the electrical energy into heat. According to Ohm's law the quantity of resistance in an electric circuit determines the amount of current flowing in the circuit for any given voltage applied to the circuit. The standard abbreviation for electric resistance is R and the symbol for ohms in electric circuits is the Greek letter omega, Ω. For certain electrical calculations, it is convenient to employ the reciprocal of resistance, 1/R, which is termed conductance, G. The unit of conductance is the mho (ohm spelled backwards) and the symbol is an inverted omega, W. To find resistance we use the equation

Resistance = Voltage / Current is used.

The resistance of an object is determined by a property of the substance of which it is made of, known as the resistivity and by the length and cross-sectional area of the object. Also other variables such as the temperature can determine the resistance. Usually, a material's resistance increases with the rise in temperature as the voltage going across the wire has to avoid the resistor's atoms more.

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The dependant variable is the length of the wire.

The controlled variables are the potential difference, the power pack, the voltmeter, the ammeter, the piece of wire used, the temperature. The only variable I am going to change is the length of the wire. I must keep all the other variables constant. If I did not then just one small change could completely change the outcome.


In order to carry out a fair and reliable test I repeated the experiment three times and then I used the mean to calculate the resistance. I decided to use readings starting from 10cm and then work upwards at a 10cm pace. By then recording ten results I am enabling myself to make more accurate results.

I will use the best apparatus available to facilitate me to obtain reliable results. For example I am going to use a brand new piece of nickel wire.


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If we were to repeat our experiment again we could use a more precise voltmeter/ammeter such as a digital one, this would give us a more precise graph. But because we used a non-digital piece of apparatus we found it harder to obtain accurate results; mainly due to having rounded to two significant figures only.

Also having the first result at 1.2 amps we were not able to set the scale to 1amps. Instead we had to set the ammeter to a less accurate scale of 5amps. However our experimental results are good enough to support our prediction and conclusion as they follow the line of best fit. However to improve our experiment we could use a digital ammeter/ voltmeter in order to obtain better results. Also we could extend the length of wire used to two metres to include more constant results.

Further experiments I could do related to the resistance in a wire would be to see whether the following variables would make a difference in the resistance of a wire:

The width: I think that the resistance would be decrease as the wire got wider, because there would be more room for the electrons to move through the wire.

Material: if I was to use different wires then the resistance would change depending on how many atoms were in the wire.

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