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Resistance of Wire Investigation

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Alexander Kilpatrick       GCSE Coursework - Plan                Page                               01/05/2007

Resistance of Wire Investigation



How the resistance of wire varies with its length.


I hypothesise that increasing the length of wire in a circuit will increase the resistance in a circuit.

Resistance involves collisions of the current-carrying charged particles with fixed particles that make up the structure of the conductors or wires.

Therefore I predict that increasing the length of wire will increase the number of times electrons collide inside the wire.

The resistance (R) of an object is measured in Ohms (Ω) and is determined by a property of the substance of which it is composed, known as the resistivity (image01.png), and by the length (l) and cross-sectional area (A) of the object, and by the temperature. At a given temperature, the resistance is proportional to the object's resistivity and length, and inversely proportional to its cross-sectional area.

This formula is:  

                        R =image01.pngl/A

It is easy to understand how the dimensions of a material affect resistance, in equation form: the longer the wire, the greater the resistance to the flow of charge.

...read more.


A) for the constantan wire is (π x 0.0002252) = 1.590431281 x 10-7 m2.The values for l are the independent variables for this experiment and can be substituted easily as we progress.

I will predict some of the resistance (R) values for the forthcoming experiment using the formula R =image01.pngl/A . These predictions will be useful for testing the reliability of the results I obtain in the experiments.

Length of wire (l) - m

Resistivity of Constantan

 (image01.png) -  Ωm at 20oC.

Area of cross-section (A) – m2

image01.pngl/A = Resistance

 (R) - Ω


4.9 x 10-7

1.590431281 x 10-7



4.9 x 10-7

1.590431281 x 10-7



4.9 x 10-7

1.590431281 x 10-7



4.9 x 10-7

1.590431281 x 10-7



4.9 x 10-7

1.590431281 x 10-7


To clarify the reliability of my experiment I will draw a graph to illustrate the resistivity of constantan. The graph will have the Restance results (R) on the y-axis, and the length divided by the cross-sectional area (l/A) on the x-axis.

...read more.


controlled variableCross-section of constantan wire. As demonstrated in the formula R =image01.pngl/A, the cross-section of the wire has a direct effect on the resistance and therefore the current and voltage. Consequently we will keep this constant as a controlled variableTemperature. This will also be kept constant at room temperature, so is a controlled variableLength of constantan wire. This is what I am changing as my independent variable

Preliminary Experiment

To ensure this experiment will work, the method is suitable and the range of readings is appropriate, I will conduct a preliminary experiment.


Length of Wire (m)

Voltage (V)

Current (A)

Resistance (Ω)



Off scale






From the preliminary experiment I noticed that the ammeter used had too small a limit (0-2 Amps) and hence the current result for 1m of wire was off the ammeter’s scale.

Therefore I will adapt my method to having an appropriate ammeter for coping with larger amounts of current, i.e. a 0-5 Amp ammeter.

...read more.

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