Apparatus
Power Supply Unit (PSU)
5 Leads
Constatan Wire
2 Crocodile Clips
1m Scale
Ammeter
Voltmeter
Cello tape (how much ever required)
Method
- Arrange apparatus as shown in the Diagram:
- Set the PSU on a low voltage so that there is not too high a current passing through the circuit because might make the wire too hot which increases resistance.
- Cut wires to the following lengths: 10cm, 20cm, 30cm, 40cm, 50cm, 60cm, 70cm, 80cm, 90cm, and 100cm.
- Attach the wire to the leads with crocodile clips.
- Take the reading from the ammeter and the voltmeter and record in results table.
- I plan to take 10 readings and repeat them 3 times. The range is 10cm to 100cm.
- Then work out the resistance using the formula: Voltage ÷ Current = Resistance
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We were told to turn the voltage to 3V so that overheating was minimized and also lengths lower than 10cm were not tried, which also helped to avoid overheating.
Factors Affecting the Results
Observation
Reliable measurements
Unreliable measurements
Analysis
Conclusion
I came to a conclusion that resistance is directly proportional to the length of the wire. As the length of the wire increased the resistance got bigger. Looking at the graph we can say that there is a strong positive correlation. When the length of the wire doubled so did the resistance. For example on the graph if we go to 10cm and go up, the resistance is 0.4hms and at 20cm the resistance is 0.8hms.
According to my prediction, an increase in length resulted in an increased resistance. If we look back into the prediction we can say that everything is made out of particles (atoms). Current travels between atoms, so the longer the wire the more the atoms. Voltage reduces as current passes because the more the atoms the more the collision with the electrons which slows the flow down which means resistance is high. So, the results that I have obtained support my prediction.
Evaluation
Mostly all results fit perfectly into my graph except for 2 anomalous. I think these 2 anomalous occurred due to overheating of wire or the equipment not giving accurate result. I think these misfit results could have been made better by repeating the results by taking care of the overheating by switching of the PSU after taking result or getting better working equipment for better results.
I think our measurements were not very accurate because of one reason. That is when we took measurements of the wire the wire was not completely straight. I did my best at that point of experiment but it did not result in the wire being completely straight. This does not have a solution. Another problem was that we had to leave extra piece of wire at the ends, so again it is not exact to its measurement. And next time it is better to take measurements to its nearest millimeter. But our results were reasonably accurate and also there were no anomalous results due to this error. The problem might have been that the voltmeter and the ammeter were not accurate to 2 decimal places which they were supposed to be. The last decimal kept flickering and that’s why we noted the readings to 1 decimal place. To make my measurements even more accurate is to use and better working equipment and also try to arrange apparatus in a way that results might be even more accurate.
Most of my results were reliable. Look back at the page ‘Observation’. The results marked in green are very reliable except for the one result marked in blue which is not very reliable. I think it one of the anomalous and caused mostly due to overheating of the wire. The only thing to be done is to remember to switch off the PSU after taking result. Also repeat readings for unreliable results to see improvements can be made. I think the rest of the results are accurate or reasonably accurate.
