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Factors Affecting the Resistance of a Metal Wire.

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Physics AT1: Factors Affecting the Resistance of a Metal Wire.


I am going to test which factors affect the resistance of a metal wire, of which there are four, these are: the length, the type, the width and the temperature of the wires. I will use the equation I=V/R to work out the resistance of the wires, after finding out the voltage when the current is altered.

I will use a variable resistor to vary the current throughout the circuit and take readings of the voltages corresponding to that current.

In order to make this experiment fair; I will keep the width, temperature and type of wire constant. I shall investigate the changes in resistance when the length of the wire varies as this is the easiest variable to change because monitoring temperature is difficult, as is being certain of the width of a wire. I am not changing the type of wire because we do not have many different types available to us in school. I will keep the current small so that the wires do not overheat; otherwise there will be another change in variables. The increase in the temperature is dangerous, which is why this variable is kept constant.

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Copper wire has a low resistance, therefore, voltages are too difficult to read, which is why this type of wire shall not be used in this experiment.

Nichrome wire of diameter 0.457mm  is the better of the three wires to use because the values are clearer to read. There is a smaller resistance and it does not exceed the maximum voltage (3 x 0.85V = 2.55V).

I shall use Nichrome wire of diameter 0.457mm for this experiment. The temperature will remain constant so this cannot affect experimental values of the resistance. I will maintain the temperature by using a low current and I using lengths of wire above 20cm to prevent the wire from overheating.

The maximum length of wire available for use is 3m (300cm). I shall use lengths 40cm, 80cm, 120cm, 160cm, 200cm, 240cm, and 280cm. This covers the majority of the wire length. I have chosen seven values because when the average resistance is plotted on the graph, it is more accurate and clearer to read.

I shall measure the voltage, and then  calculate resistance, for each current three times in case any anomalies appear. Should there be an anomaly, I will take the average of just two values and exclude the anomaly.

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The voltages in my table hardly ever reached over 2V so if I carried out this experiment again, I would prefer to use a range of sensitivity 2V for more accuracy.

This experiment could be carried out using data-logging to both speed it up and to give more accuracy. I could also use different wires to see if my conclusion is true for other types of metal wires.

The points plotted on my graph were very close to my line of best fit, proving that the length of wire and the average resistance are directly proportional.

There was one anomaly within my results, which I have highlighted. When the reading was taken, the wires were touching, causing it to short-circuit. Next time, for more accurate results, I would make sure the wires were not touching.

For greater reliability, I could do more repeats, although I think if I did do more repeats, they would be very similar to those I have already taken.

I think my evidence is sufficient to support a firm conclusion that resistance is directly proportional to the length of a metal wire.

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