Preliminary Experiment - testing the resistance of a wire.

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Lydia Boast                                                                            29th April 2003

Preliminary Experiment.

Before starting my preliminary experiment I had to choose my wire, I decided to use Constantan because I wanted the resistance to stay the same even if the wire did get quite hot, and even though the Constantan does change if the wire gets very hot, I am not planning on letting it get this hot as this would be a risk. As you can see compared to two other resisting components, it stays the most constant in its resistance.

I have also decided the thickness of my wire; I looked at a range of thickness’ and eventually decided on 28swg. I decided this because the thinner wire, 36swg, was too thin and would snap very easily when doing the experiment, which would mean you would have to keep on changing your wire giving you useless results. The resistance for the thin wire is too large for this experiment. The thicker wire, 16swg, was too thick as it had a lot of kinks in it that you wouldn’t have been able to get out, the resistance was too low for the thick wire as well. I am not going to measure to smaller lengths of wire, as the resistance difference in them would be too small to measure. From the results that I got in my preliminary experiment I have decided to measure the resistance going up 10 every time.

I have decided to use 0.8 as my current as this worked best with my wire in my preliminary experiment. It also means that my maximum voltage is low enough not to overheat the wire and cause any injury.

My variable is going to be length, I decided to use this, as it is easiest to measure and seems to have a significant effect on the resistance as you can tell from the results from my preliminary experiment. I am going to keep the thickness of the wire; the type of wire and the current constant as if any of these changed then it would ruin the experiment.

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My prediction is that the longer the wire, the bigger the resistance as this is what has happened in my preliminary experiment.

Planning.

Circuit Diagram:

Apparatus:

Power pack, DC supply

Constantan wire, 28swg, 1.5m

2 crocodile clips

1 metre rule

1 Voltmeter – the highest voltage this will go to is 5.76 volts

1 Ammeter – set at 0.8 amps

Method:

  1. I am going to set up my circuit from my circuit diagram.
  2. I am going to ...

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