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Investigation to show how the length of a wire affects the resistance.

Extracts from this document...

Introduction

Investigation To Find Out What Factors Affect The Resistance Of A Wire.

Aim.

To investigate and find out how the resistivity of a wire is affected by altering the lengths of constantan wire.

Prediction.

The longer the piece of wire, the greater the resistivity.  This is due to the idea of free moving electrons being resisted by atoms in the wire.  In a longer piece of wire, there would be more atoms for the electrons to collide with and so the resistance would be greater.  The relationship between the wire length and the resistance should be directly proportional.

For example if I had a 30 cm wire and a 60 cm wire, the 60 cm wire would have a resistance twice that of the 30 cm wire.  This is because in a wire twice the length there would be double the amount of atoms colliding with the electrons, and therefore causing twice as much resistance.

The resistance can be calculated by using the formulae:

R=V/I         RESISTANCE(R)=VOLTAGE (V) /CURRENT (I)

Resistance is measured in ohm’s (Ω); Voltage in Volts; Current in amps.

Flow of electrons.

1. Electrons colliding in to atoms causing energy to be lost in the form of heat, and resulting in the increase of the resistance.

Flow of electrons.

Middle

Then work out the resistance by using the formulae V/I=R (Voltage/Current = Resistance).Plot graph to show average current against the wire length.Plot graph to show average resistance against the wire length.

Fair test.

• The same voltage was used for each experiment (2 volts).  This was done by using a variable resistor.
• The same piece of constantan wire was used for each experiment.
• The same voltmeter was used.
• The same ammeter was used.
• The same power pack was used.
• The same connecting wires were used.
• The power was left on for the same amount of time (30 seconds).

Conclusion

Evaluation.

The experiment proved to be a success and I retrieved an accurate set of results although some results were not as accurate due to faulty/damaged voltmeters and ammeters.

Measuring the lengths of the wire was also an inaccuracy as the rulers used were not exact, and it was difficult to get an accurate reading of length by eye, as the wire may not have been completely straight.  These would have also contributed to the error. These results would be difficult to improve on as they are reasonably accurate, and there were no anomalous results.

If I were to do this experiment again, I would use newer, more accurate ammeters and voltmeters, a more accurate method of measurement, and take a much wider range of readings, and more readings so that a more accurate average can be taken.  I would also investigate other factors, such as temperature, voltage and current, and see how these affect the resistance.  I would also use a different type of wire thickness etc. and see what difference that would make to the resistance which would make it much more interesting.

As these results had a range of only 5 readings, from 0-50cm, and were only repeated three times, I would say that these results are not strong enough to base a firm conclusion on because there are so many potential sources of errors.

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