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Factors Affecting the Resistance of a Wire.

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Factors affecting the resistance of a wire.

Aim: to find out if and how the length of a wire affects the resistance of a wire.

Theory: Resistance is anything in a circuit that restricts the flow of electrons. It doesn’t slow them down. As the electrons pass through a wire or component energy has to be lost.


Above is a piece of wire with its atoms and electrons passing through it. When the electrons hit the particles in the conductor, they transfer some of the energy to the particles on the conductor this causes them to vibrate faster therefore the conductor heats up.

Ohms Law is when a conductor is kept at a constant temperature the current flowing through the conductor is directly proportional to the P.D. (potential difference) across its ends.

Resistance is calculated by dividing the voltage by the current.


This triangle shows how to work out Resistance in ohms

V = R


                                                It also shows how to work out Voltage in volts.

        I x R = V

        As well as how to work out Current in ampere        

V = I


There are 4 main factors effecting resistance, they are:

  1. Temperature.
  2. The cross sectional area.
  3. The material.
  4. The length.

As the current increases, so does the temperature of the conductor, because the electrons moving through it faster.

...read more.



I have chosen to use Manganin as my wire because its resistance is constant at all voltages which shows that its tempreature doesn’t increse much when the electrons flow through it. Which shows that it would give me more acurate results when it comes to finding out if and how the length of the wire effects the resistance because it will keep the tempreature constant at hight voltages. It also has the most consistant results.

Prediction: I predict that the longer the wire the higher the resistance. This is because the electrons have further to travel and more atoms to bump into.

I found a formula called the resistivity formula in a text book. The formula was.

R ∝ L

R = Resistance

L = Length (15cm)

This means that resistance is proportinal to length.

To work out the resistance you need to add a constant and the cross sectional area of the wire. So the formula looks like this:

R = PL


P = Constant

A = Area (Cross sectional)

The constant for Manganin is 44 x 10-8  which is = 0.000000044

I have chose to use Manganin 24 SWG. The diameter for this is  0.56mm


Therefore the radius is  0.00028

The formula to work out the area of a circle is ∏r2

∏ = 3.141592654

         r = 0.00028

         r2 = 0.0000000784

∏r2 = 0.00000024630064

         A = 0.00000024630064

...read more.


Evaluation: this experiment went quite well it helped support my theory and prediction. It does this by showing that the resistance is related to the length it also supports that it is directly proportional.

As you can see form my results and graphs the accuracy of my experiment was quite good except for a few exceptions like the 50cm wire which was most probably measured inaccurately therefore giving a bad result.

My results are enough to support my theory that there is a relationship between the length and resistance as shown by my line of best fit. Also my results for the 60 and 70cm wire were exactly as I had predicted this is shown in my results table in the “How far off are my results.”

To improve this experiment if I was to do it again I would use a different wire each time as in this experiment when id done the 10cm wire it would let it cool down if it was hot and use it again this could have made my experiment inaccurate as damage could have been caused to the wire when I first used it. So next time I would cut another wire and use that one. If I had more time I could have done the experiment until I got a constant not an average this would have been more accurate as I would have had more results to back up my prediction and theory.

...read more.

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