Resistance of a wire!? Watch

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Report Thread starter 14 years ago
Hello im currently doing my GCSE Physics Coursework and i have to carry out an investigation of the resistance of a wire i have three variables which i can choose either:

Cross sectional Area

I was planning on picking the 'length' variable but im not too sure if its the best i could also choose the 'cross sectionaral area' variable!

What do you think? Which one would be the best to gain more marks and to make it easy and reliable to get good results?

Thanks for your time

From John Wood
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Report 14 years ago
it should be fine..

and in Evaluation u can write about how oyu cud extend the investigation by varying the xsectionalarea and also material.
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Report 14 years ago
Use the length. It would make your graphs look much neater. This is because the resistance of a wire is directly proportional to its length.

This proportionality can be shown when you plot the results for the resistance of the wire (on the y-axis) against its length (on the x-axis). If the two plotted variables are proportional to each other then the line shall pass trough the intercept and have a constan gradient.

Look up something called "Resistivity". Basically, it is like a resistance to electric current factor in wires of different materials. The formula is actually:


I just think if you look up what it is it will help you to understand it more. Although because it is not on your GCSE syllabus I wouldn't mention it.

Now apply your GCSE Mathematics. You know that:

y=mx+c : In this case you are plotting y against x

Compare that to: R=((pl)/a)

Because you are plotting R against l this means that R=y AND l=x

In fact therefore:


Intercept at the origin because c=0.

So just mention that after doing a bunch of results for the same wire, where you were just varying the length, and after having a plotted a graph for R against l you noticed that the resistance of the wire is directly proportional to its length.

Proportionality means that when y is prop. to x y=kx where k is the constant of proportionality.


To get extra marks you could also do a few experiments where you are varying the cross sectional area of the wire. Now plot R against the cross sectional area of the wire. You will get a graph that gives high resistance when the area is low and low when high. Look at the graph... Look at the gradient.

Comparing to y=mx+c R=((pl)/a) something should tell you. You will see that is inversely proportional to a => R=(k/a) where in this case the constant of proportionality is pl.

So just same that you used a wire of the same material and you found out that:

Its Resistance is directly proportional to its length (i.e. the longer the wire is the bigger the resistance)


Inversely proportional to its area (i. e. the bigger the area the smaller the resistance).

Remember and mention this; throughought you have used wires of the same material, and when you were verying the length you kept the wire of the same area, and when you were varying the area you were experimenting with the same length.

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