To make sure the main investigation would be successful, we needed to determine which wire to use, the minimum length we would work with and the voltage we would use

Aim

To see if changing the length of a wire changes the resistance of the wire.

Preliminary Experiment

Aim: To make sure the main investigation would be successful, we needed to determine which wire to use, the minimum length we would work with and the voltage we would use; too high would cause the wire to heat and too low would have too little an effect. To choose these variables we carried out a preliminary experiment.

Diagram:

Table:

Wire

Diameter (cm)

Length (cm)

Voltage (V)

Did the wire heat?

Bare (dia 24 SWS)

0.05

5.0

6

Yes, and it glowed

Bare (dia 24 SWS)

0.05

5.0

3

Yes

Bare (dia 24 SWS)

0.05

5.0

2

Slightly

Bare (dia 24 SWS)

0.05

0.0

3

Slightly

Bare (dia 24 SWS)

0.05

0.0

2

No

Conclusion: From our preliminary experiment, we decided to use 2V. When we tested 3V, the wire was beginning to heat, (which we tested by holding a piece of paper near it and seeing if it had any effect) which could have been a separate factor for the resistance changing which would have made our results unreliable and inaccurate. This would have an effect because the electrons move quicker through the wire the higher the temperature gets. However, when we used 2V, the wire did not heat for the 10 cm sample, but the readings on the voltmeter and ammeter were still sensible and would be easy to work with.

We also decided to stick with the first wire we tested as it worked well, although our minimum length for the wire will be 10 cm because the wire got too hot with all different voltages for the 5 cm pieces.

Resistance Investigation 2