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does the resistance change in a wire if you change the length of it!i know it sou.... watch

1. hiya everyone i am doing a science investigation on how the resistance changes in a wire if you change the length!i was wondering is it a amp metre and a volt metre u use? i cant remember
2. The resistance R of a length of wire L with cross sectional area A is given by:

R = kL
......A

k is a constant called the resistivity and is specific to the material from which the wire is made.

(the dots are there to align the A correctly - they are not part of the formula)
3. Sorry - I got sidetracked and didnt finish the post,

You can use an ammeter (that is the correct spelling) and a voltmeter to measure both the current through the wire and the voltage across it. If you use Ohm's law, R = V/I, you can calculate the resistance.

Try comparing the resistance you measure to calculated values of R using the formula I gave in the last post. You can find the resistivity of common wire materials, such as copper in textbooks and on the internet.

Hope this helps.
4. thankyou but ive lost all my work!once you have done the brief,prediction,table of results(3 times and average)equipment and how to make it a fair test what do you do then?
5. OK. Now you need to draw a graph of results. Plot the current along the x axis and the voltage on the y axis. Mark on the points for one particular length and draw a line of best fit. This should be a straight line passing through the point (0,0). Repeat this for the other lengths of wire you used, plotting all of the graphs on one sheet of paper. You should find that they all produce a straight line through the origin, but they have different gradients. Obviously the line with the steepest gradient corresponds to the resistance of the longest wire. Now calculate the gradient of each line you have drawn. These are the resistances of the wires. Plot a graph of length of wire along the x axis with resistance on the y axis. The gradient now will be the ratio k/A. If you know the cross sectional area you can use this to find the resistivity of the wire (constant), and check that it matches with a databook value. If you have not measured the cross sectional area of the wire, you can just see that the graph of R against L is a straight line going through the origin. This suggests that the resistance of a wire increases linearly with length.

After this you need to evaluate your results and make some conclusions.
6. these are my results :-

Length A V
0.10cm 1.19 0.71
0.20cm 1.07 0.89
0.30cm 0.96 1.28
0.40cm 0.87 1.29
0.50cm 0.75 1.51
0.60cm 0.65 1.71
0.70cm 0.61 1.81
0.80cm 0.56 2.01
0.90cm 0.44 2.15

Length Resistance
0.10cm 0.71/1.19= 0.596Ohms
0.20cm 0.89/1.07= 0.831Ohms
0.30cm 1.28/0.96= 1.333Ohms
0.40cm 1.29/0.87= 1.482Ohms
0.50cm 1.51/0.75= 2.013Ohms
0.60cm 1.71/0.65= 2.630Ohms
0.70cm 1.81/0.61= 2.967Ohms
0.80cm 2.01/0.56= 3.589Ohms
0.90cm 2.15/0.44= 4.886Ohms
i am now evaluating my results as you can see most of them are accurate but what can i say to say that some of them arent i cant think of how to word it??any idea's
7. In the case where some results are not accurate you need to wheel out the standard excuses:
• Human error
• At larger voltages the wire heats up and lengthens, so the resistance increases

The second point explains why your final value is too high. I would perhaps put the fourth value down to human error. When plotting the line of best fit, ignore the fourth and last points.
8. I hope this is useful.
9. thankyou v much for your help x x
10. is this alright could you think of anything else to say:- sorry its just im taking half of today of to do this its got to be in school by 3:30!
11. think that most of the experiments results were accurate but I think I can put the last result I had (0.90cm) down to human error as I think this result was because the wire was probably a lot hotter than to start with and I may have forgotten to take it of this last time as I was in a rush, I think this as I’ve already stated if it gets to hot energy would be given of as heat causing the resistance to increase, which is what I think happened here. Also the difference between the resistance in 30cm and 40cm are quite similar I think this is down to human error as I should of waited a bit longer when recorded my results as I didn’t give the voltmeter and the ammeter enough time to get to the result it should of, because I may of taken the wire and crocodile clips of to get onto the next results.

WHOOPS FORGOT TO PUT IT THE FIRST TIME!

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Updated: December 4, 2003
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