I think when we use longer lengths of wire the resistance will increase because has mentioned the wire has resistance so when using a longer length of wire the current as to overcome more resistance. I also think that when we use a larger diameter wire the resistance will decrease because the current can spread out over the wire more so there is less chance the metal atoms in the wire will get in the way of the electrons.
Ohms Law gives a relationship between Voltage (V), Current (I) and Resistance (R).
Apparatus
The apparatus we will use is:
Power supply, voltmeter, ammeter, wires w/connectors, 28 constantan, 34 constantan wire.
Preliminary Test
To help me find a suitable current to use in the main investigation that doesn’t heat up the wire.
Method:
- Setup apparatus as shown in the diagram.
- Using a variable resistor, increase the current until a heating effect is observed in the wire.
Result:
At below 0.2A no heating effect was observed.
Conclusion:
A current of less than 0.2A will be used for the main investigation, so that no heating effect in the wire will affect the resistance.
Method (Main Test)
- Set the equipment up as shown in the diagram.
- Switch the power supply on and set it to 4 volts.
- With the length of the wire at 100cm record voltage and keep current constant using rheostat.
- Repeat for 80cm, 60cm, 40cm, 20cm and 0cm of wire.
- Work out resistance using ohms law, resistance = voltage/current/
- Repeat investigation another three times.
Fair Test And Number Of Readings
To keep our experiment as fair and as accurate as possible I only changed the independent variable (the length of wire) and kept the temperature and type of wire the same (controlled). I repeated the experiment 3 times as I can work out an average set of results without any anomalous readings.
I took 5 readings (100-0) on each experiment so I got a good range of results I can get a good average from.
Safety
- General safety when using electricity.
Making Observations
To get accurate results we repeated the experiment 3 times for each type of wire. However we did find one anomalous result the second time we repeated the experiment for the 34 constantan wire. To get around this I will not include that result in the averages.
Results
28 Constantan
1)
2)
3)
Constantan 34
1)
2)
3)
Conclusion
Firstly I found that when using larger lengths of wire the resistance increased. I found this to be the same for both constantan of wires. This is what I predicted because the current has to overcome more resistance when flowing through a larger length of wire. I also found when using a smaller diameter of wire, the larger the resistance. This did agree with my prediction and theory.
Evaluation
I think we got a relatively good set of results, which agree with my prediction and theory from the text books. However we did find one anomalous result but this did not affect the average results. To improve our investigation I think we could have used the exact same equipment each time as each may differ slightly. I think our results are accurate and that if we did the investigation again we would get approximately the same results.
I could extend my investigation by using a different type of wire not including diameter. Yhis wire could be made from a different type of metal.
