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Variables That Affect the Resistance of Wire Course Work

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The four factors that affect the resistance of a straight piece of wire:

Temperature                                                                                                      Type of metal

From considering all four variables and how I would carry out this investigation, I have decided to use the length and diameter as the two variables.


The aim of my investigation is to investigate how length and diameter affect the resistance of a straight piece of wire.

Metals as conductors

Electrons do not stick to the atoms in a metal very well and so there are many free electrons in the metal, this is the reason why metals such as copper are very good at conducting electricity.


Resistance is caused when the free electrons in a wire have to jump past and accidentally collide with other atoms in order to pass through. It is the force, which resists the flow of electrons around an electronic circuit so that more energy is required to push the charged particles around. The jumping and collisions of the electrons and atoms causes the resistance. Resistance is measured in ohms.

Wire length: As the length of the wire increase, I believe that the resistance will increase.

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Main experiment

First, the circuit was set up as shown above. I had to be careful in connecting circuit, because the Voltmeter had to be placed in parallel and the ammeter, which had to be placed in series. Draw up a rough table onto a piece of paper with the appropriate headings. The wire was set on to a metre rule so the crocodile clips could attach onto the wire, making the results more accurate.

Basic method

To carry out this experiment, the power supply was switched on and adjusted to the appropriate Amp. To do this the slider on the variable resistor was moved up or down to increase or decrease the current. When the appropriate Amp was set, the voltage was read on the voltmeter. I could then use these two figures to work out the resistance.


Length: 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. Therefore, if the length is doubled the resistance should also double.

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To also improve on my results I could use a digital device that would directly measure the overall resistance of the wire thus getting rid of the voltmeter and ammeter and also the arithmetic required to work out the resistance (r=v/i). The graphs shows that my results are quite reliable as there are only a few anomalous points, to improve the reliability of my results, I could also have repeated the same lengths of wire more times. Although the wires diameter measured 0.28, the thickness of it may vary by a small amount and maybe helping to cause the anomalous results. Sometimes the voltmeter flicked between a decimal point, I maybe could have thought it was the wrong number and therefore would have ended up with the wrong average resistance, to eliminate this particular problem; I could have used a voltmeter with at least three significant figures after the decimal point. In the experiment, I did not control the room temperature but instead just assumed it was keep constant throughout my experiment; this could have made the wire get hotter and therefore making my experiment not as accurate. In future experiments I would control this variable factor and make it constant.

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