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What Factors affect the resistance of a wire?

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In this investigation I will be exploring the factors that affect the resistance of a wire. Resistance is a force which opposes the flow of an electric current around a circuit so that energy is required to push the charged particles around the circuit. The equipment I will use to carry out each experiment is:

-A power pack

To give the circuit electrical energy..

-An ammeter

To measure the current and in turn work out the resistance of each wire.

-A voltmeter

To measure the voltage and use it with the current to fond the resistance of each wire.

-Selection of wires

different materials, widths and lengths to compare the ways in which they affect the resistance.

To connect the other equipment together and to complete the circuit.

-Crocodile clips

To connect the wire being investigated to the rest of the circuit and to change the length of the wire i.e. I will clip the wire to the length I want to measure.

-1m ruler

 To measure the wire being tested to ensure a fair test.

Here is a diagram of the circuit I will use to find the voltage and current readings of each length wire:

I will be using Ohm’s law, R=V/I, to find the resistance of each piece of wire.


To obtain results to compare the factors that affect the resistance of a wire, I am going to set up the circuit above, using a voltmeter in parallel to measure the volts and an ammeter in series to measure the amps (current). The factors I will be comparing are the length, width and material of a wire.

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I am not going to be comparing the affect of the temperature on the resistance, because we do not have the correct equipment to give an accurate temperature reading or to keep the temperature constant, but if I did compare the temperatures, I predict that the hotter the wire, the more resistance there would be. I think this because heat in metals causes the atoms to vibrate more by giving them more energy. More vibration makes atoms "get in the way" of the electrons more often. The electrons then must spend extra time on deflected courses instead of going straight ahead. Current can sometimes cause the wire to get hot; this would increase the resistance. That is why I am going to turn the power on for five seconds only, to try and prevent the data from being distorted by the temperature.

Now that I have discussed the variables I will be researching, I need to state exactly which lengths, widths and materials I will use to obtain good results.

Lengths (in cm):        Widths (in mm):        Materials:

(All materials)                Constantan                Constantan

10                        0.20                         Copper

20                        0.315                        Nichrome

30                        0.56

40                        Copper

50                        0.274

60                        Nichrome

70                        0.28


I will repeat each experiment 3 times and take an average of the results to improve accuracy and to make my results more reliable. In addition, I want to know what voltage to set the power-pack to to give a fair reading but not allowing the wire to get too hot.

Preliminary experiment.

I am now going to do some preliminary tests to see if any amendments can be made to my method and to check that the circuit and method are both fair and safe. It will also give me an idea of whether my predictions are correct or not.

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From doing this experiment I have come to the conclusion that the longer the wire is, the more resistance there is, with the length increase proportional to the resistance increase. Also, the width of the wire is inversely proportional to its resistance, and so the wider the wire is the less resistance there is. The final conclusion I have drawn is that the order of resistance in the wire is nichrome, constantan, copper, with nichrome having the most resistance.

abby brakewell 11B. Physics coursework- resistance of a wire.

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