The Electrician's Dilemma

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The Electrician's Dilemma

An electrician has been asked to repair an old radio. He believes that

he needs a resistance of 1.9 ohms which is not easily obtained.

You are provided with some reels of resistance wire and are asked to

plan and carry out an investigation to help the electrician solve this


When your investigation has been concluded you discover that a

resistance of 28.5 ohms is also required to complete the repair. Show

how you use the data from your investigation to also obtain this



As mentioned in the previous page, an electrician wants two

resistances: 1.9 ohms and 28.5 ohms. I am to find out how to do this.

I will be provided with different reels of wire of constantan, each

reel having a different diameter. I will, for three different

diameters, find the resistance of the wire at different lengths. For

example, I will take the 24 gauge wire (0.56mm diameter) and find its

resistance when it is at 100cm, 80cm, 60cm, 40cm. Exactly how I will

do this will be in my method.

I will then plot a graph of resistance (Ω) against length (cm). From

the graph I should be able to read off what length is needed to create

1.9Ω. Then finding and using the equation of the graph I will be able

to find what length is need to create 28.5Ω.

I will then be able at the end to say:

" you need ….. cm of ……gauge constantan wire to create a resistance of


I will through this investigation also identify patterns and etc. of

how length affects resistance. In addition I will also hopefully find

how diameter affects resistance.


Preliminary work

Ohm's Law

To solve the electrician's problem, I will investigate relationships

between length of wire and resistance. Several of ' Ohm's laws' are

extremely relevant to this investigation.

Ohm's law states that current through a metallic conductor

(E.g. constantan wire) at a constant temperature is directly

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