# Resistance of a Wire

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Introduction

## Physics Investigation: Resistance of a Wire

I have been asked to solve the problem of getting a resistance of 1.9 ohms using resistance wire. Resistance is how easily a potential difference is carried across a conductor. The higher the resistance, the bigger the potential difference has to be to go through the conductor. To do and understand this investigation I must see firstly what factors are involved when looking at resistance. I have come up with six things which affect the resistance in a wire:-

## Thickness-

If the wire is very thick i.e. it has a big cross sectional area (csa). It will have a smaller resistance than one with a smaller csa. This is because electric current in a metal is made up of electrons jumping and hitting more electrons, like dominoes. The metal ions in the wire block some electrons, causing a resistance. If there is a bigger area through which the electrons have to squeeze, the resistance will evidently be lower.

## Material of Wire-

This is quite an obvious one, as I know that all materials have different conductivity. For example copper is a better conductor than tungsten but silver is the best. By knowing what the conductivity of a material is, I know how much resistance it would have, as the better the conductor the less the resistance.

## Temperature-

Middle

20

30

40

50

60

70

80

There should be 3 such tables, and one with just the average resistance and length.

Length (cm) | Average resistance (Ohms) |

I know of the link between potential difference, current and resistance. It can be written in the form

R = V/I. This is the equation I must use to find the resistance for my results. As I have said above, I think there should be a direct link between resistance and length. I know there should be a basic link because of the electrons that make up an electrical current. They have to get past the ions in the metal, and the longer the wire is, the more ions there are, so the bigger the resistance is against them. I also think there will me more of a direct link between length and resistance. I can show why I think this using my scientific knowledge:

Resistance = conductivity X length / cross-sectional area

In my experiment the conductivity will always be the same, as I will only use one type and material of wire. Also, since I am using one type of wire, the cross sectional area will remain constant. Therefore I can rewrite the above equation as:

Resistance = k X length (where k is a constant) or R L

I can replace the conductivity and the cross-sectional area because they will remain the same.

Conclusion

Apart from this error, I did not find anything else significantly wiring with my experiment. There was, however, one strange result. In my graph, I drew the line of best fit to fit as many points as I could while still going through the origin, but there is one point which didn’t fit. This could just have been my line, maybe the results weren’t accurate enough to go through the origin. Or it could have been that my measuring was not accurate enough first time; that I didn’t measure 10cm exactly enough and so came up with an anomalous result. To overcome this I could haven used a more exact ruler. However I think that my results are accurate and reliable enough to support my conclusion.

One way to further this investigation would be to see how the width of the wire affects my formula. I think that as the width got smaller, the resistance would increase. This would be because of the original formula Resistance = conductivity X length / cross-sectional area. As the width got smaller, cross-sectional area would get smaller, and by dividing by a smaller number would give a bigger resistance.

GCSE Physics Investigation

The Electrician’s Dilemma

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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