To find out how the length of a wire affects its resistance by carrying out an investigations

Coursework

Resistance in a wire

Aim:

To find out how the length of a wire affects its resistance by carrying out an investigations.

Background Information:

Resistance occurs when the electrons travelling along the wire collide with the atoms of the wire. These collisions slow down the flow of electrons causing resistance. Resistance is a measure of how hard it is to move the electrons through the wire. Measurements of electrical resistance is taken in ohms, the formula for working out resistance is:

Resistance = potential difference / current

To measure current you place an ammeter in series with the components.

Potential difference is measures by using a voltmeter in parallel with the components. Resistance is anything in a circuit which slows down the current.

Preliminary Experiment:

For my preliminary experiment is with a meter ruler with a wire stuck to it, so it can be measured. It will be connected to a power supply of 2v then have a voltmeter connected in parallel and an ammeter connected in series to the wire. I will then change the length of the wire to find out the lowest and highest results for current and potential difference.

Results:

Prediction:

I predict that if the length increases then the resistance will also increase in proportion to the length. I think this because the ...

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Preliminary Experiment:

Results:

Prediction:

I predict that if the length increases then the resistance will also increase in proportion to the length. I think this because the longer the wire the more atoms and so the more likely the electrons are going to
collide with the atoms. So if the length is doubled the resistance should also double. This is because if the length is doubled the number of atoms will also double resulting in twice the number of
collisions slowing the electrons down and increasing the resistance. This is backed up by the results of my preliminary experiment.

Method

In this experiment I will select a wire that will be used in my main experiment when investing the connecting between the length of the wire and the resistance of the wire. To ensure a fair test whilst carrying out my preliminary experiments I am going to be very careful when selecting my independent variables which are the width of the wire and the wire material. I am going to use a constant voltage of 2 volts and the same material, which is Nichrome.

Meter ruler: To measure the wire being tested. Nichrome wires: Same width of wire and same material but testing different lengths. Crocodile clips: To connect the wire to the rest of the circuit. Voltmeter & Ammeter: To measure the resistance. Wires: connect the above items and to make a circuit.

In my main experiment I have chosen to use an ammeter and voltmeter, I have done this so that I can work out the resistances from the volts and amps. I shall calculate the resistance of the wire using the equation below.

RESISTANCE = VOLTS / AMPS

I have chosen to use thin Nichrome wire because from my own knowledge I know that this type of material and thickness will have the most resistance and therefore it will be easier to measure and differences in resistance.

Results:

LENGTH 20 cm 400 cm 60 cm 80 cm 100 cm
VOLTS (v)| 1.6 1.5 1.6 |1.7 1.7 1.7 | 1.8 1.8 1.8 | 1.9 1.8 1.8 | 1.9 1.9 1.9

AMPS (I) 20cm 40cm 60cm 80cm 100cm

|0.61 0.60 0.61|0.35 0.35 0.34|0.23 0.24 0.24|0.18 0.19 0.18|0.14 0.15 0.15

RESISTANCE (Ohms) 20cm 40cm 60cm 80cm 100cm

|2.6 2.5 2.6|4.8 4.8 4.8|7.6 7.6 7.6|9.9 9.8 9.8|12.8 12.8 12.8
AVERAGE RESISTANCE
2.6 4.8 7.6 10.0 12.8

From these results I have drawn a graph of the length of the wire and the resistance of the wire.

From the graph on the excel page I can see that the resistance of the wire is proportional to the length of the wire. I know this because the Line of Best Fit is a straight line showing that if the length of the wire is increased then the resistance of the wire will also increase.