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Factors Affecting the Resistance of a Wire.

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Introduction

FACTORS AFFECTING THE RESISTANCE OF A WIRE

Resistance is measured in Ohms (Ω)* and the amount of resistance determines how much current is allowed to flow by a component. Electricity is conducted through a conductor, in this case wire, by means of free electrons. The number of free electrons depends on the material and more free electrons means a better conductor, i.e. it has less resistance. For example, gold has more free electrons than iron and, as a result, it is a better conductor. The free electrons are given energy and as a result move and collide with neighbouring free electrons. This happens across the length of the wire and thus electricity is conducted. Resistance is the result of energy loss as heat. It involves collisions between the free electrons and the fixed particles of the metal, other free electrons and impurities. These collisions convert some of the energy that the free electrons are carrying into heat. There are several factors that affect the resistance of a wire.

Length

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Middle

* Ohm's Law states that the current through a metallic conductor (e.g. wire) at a constant temperature is proportional to the potential difference (voltage). Therefore V¸ I is constant. This means that the resistance of a metallic conductor is constant providing that the temperature also remains constant. Hence, the resistance of a metal increases as its temperature increases. This is because at higher temperatures, the particles of the conductor are moving around more quickly, thus increasing the likelihood of collisions with the free electrons.

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I am going to investigate how the length of a wire affects its resistance. This is the circuit that I will use to measure both the current through and the voltage across the wire. For this I am using a Voltmeter and an Ammeter. I have performed a preliminary experiment (and set up this test circuit independently) in order to establish how many readings to take across a meter (m) and I have found that taking readings every five centimetres would be sufficient.

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Conclusion

There is one truly anomalous result and that was for a piece of wire of length 15cm. For this mistake I can only blame meter inaccuracies (if I had a more precise meter that went to ten decimal places instead of two then all of the results would have been more accurate), loss of detail through gaining averages and possibly human error in reading the meters or in the calculations. If I had used a more accurate meter that allowed me to measure current and Voltage to eight decimal places instead of two then all of my results would have been more accurate.

Evaluation

I feel that my results are reliable enough to support my predictions and conclusions.If I was to do this experiment again I would make would be to use pointers instead of crocodile clips , I would do this because pointers would be more accurate. The pointers would be more accurate because the tips have a much smaller area than the crocodile clips giving a more accurate measurement of the length of wire. The wire measurement was not correct. The solution to this is to measure the lengths more carefully and ensure that the wire is pulled tight against the metre rule.

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