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Investigation in resistance in wires

Extracts from this document...


Lewis Jolly/Physics/10SC5/A12

Investigating Resistance in Wires


In this investigation I will be looking into the theory of resistance and current in wires; this theory is called Ohms Law. By doing the experiments I will be hoping to prove Ohms law correct, and testing to see if it remains constant as the voltage, and wire lengths vary.

Related Theory

Resistance is measured in ohms (image08.png), resistance can be calculated by using the formula V = I × R

V = voltage measured in volts (V)
I = current measured in amps (A)
R = resistance measured in ohms (image08.png)

This is the formula called Ohms Law. Ohms law is the relationship between voltage, current and resistance. For a metal conductor at a constant temperature the current is directly proportional to the voltage. This means that if the current increases the voltage will also increase in the same proportion. For example: If a cell provides a voltage of 1 volt and the circuit has a resistor of 1 ohm connected to it an ammeter would read 1 amp. If the cell was replaced with a 2 Volt cell the ammeter would read 2 Amps.

Resistance is caused by electrons bumping into ions. If the length of the wire is doubled, the electrons bump into twice as many ions so there will be twice as much resistance. If the cross-sectional area of the wire doubles there will be twice as many ions and twice as many electrons bumping into them, but also twice as many electrons getting through twice as many gaps. If there are twice as many electrons getting through, as there is twice the current, the resistance must have halved. This all applies if the temperature of the conductor is constant so I will have to look into how to keep it that way.

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Graph Interpretation

By looking at the graph you can see that Voltage and Current are proportional. I was unable to do repeats as I did not have enough time, this makes the test unreliable. But even though there were no repeats on all three tests from 1V to 8V there is a straight line just as I predicted. Although there were no obvious outliers, I cannot point any out due to the fact that there is nothing to compare it to.

Graph Conclusion

During the preliminary you could see, feel and smell that the nichrome wire got very hot, this was a major problem because the temperature had to be constant. The resistance of a wire is only constant if the temperature remains constant. If the temperature changes the resistance changes and so the results would be affected. The reason why the wire got hot is because we exceeded the current carrying capacity of the wire. Each cable has a rating of how much current it can carry before over-heating. We tried to pass too much current through and too short piece if wire. If we had made the wire thicker or reduced the current, the wire would not over heat. I decided to change the lengths of wire; this would increase resistance which would lower the problem of heat also I noticed that the data was too close together when I plotted the graph therefore I will make the intervals between each length 5cm rather than 2cm this will give me a clearer picture when plotting my results in a graph; the tested lengths were 20cm, 25cm, 30cm, 35cm, 40cm, 45cm, 50cm, 55cm and 60cm. I also lowered the differences in voltage: 0v, 0.5v, 1v, 1.5v, 2v, 2.5v, 3v, 3.5v, 4v, 4.

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  • Also to reduce heat I could use a wire with a larger diameter this would decrease resistance in the wire therefore reducing the heating effect.
  • If I wanted to keep the same wire lengths, same voltages, and same current the only way I could reduce heat effectively would be to increase the diameter of the wire. This would increase the cross-sectional area therefore reducing resistance which as explained earlier means that there will be less collisions between elections and ions therefore reducing heat.
  • In addition I could use a wire with a lower resistivity; the lower the resistivity the lower the resistance therefore the lower the heat.
  • The formula for power is P = I^2 x R

P = Power

I = Current

R = Resistance

This means that if I reduce the resistance then I reduce the power. Therefore if I reduce the power then the heat will be lower as well.

I can happily say I feel my conclusion is strong and I feel my data and tests have agreed with my hypothesis, although there are certain outliers I was able to retest them and single them out, I did not include them in my range bars or my averages, I can also see how accurate my results are by looking how close the lines of best fit are to the range bars and I feel that they are reasonably close, when Ohm’s Law applies the lines should be straight which they are, I feel I used enough accuracy and precision with the apparatus I used to get a good clear set of results, although I’m sure about the 55cm and 60cm calculations which I would like to retest using milliamps as a measurement I still feel I collected enough correct evidence to feel strong that my hypothesis was correct, and that my conclusion is correct too.

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Here's what a star student thought of this essay

5 star(s)

Response to the question

You have answered the question set very well, with deep understanding and explanation throughout. All steps of the investigation are well detailed and explained, with suitable diagrams to assist the text. A photograph of the apparatus used would complement the ...

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Response to the question

You have answered the question set very well, with deep understanding and explanation throughout. All steps of the investigation are well detailed and explained, with suitable diagrams to assist the text. A photograph of the apparatus used would complement the circuit diagram well. The piece is also missing a graph of the results rather than just a predicted graph, as there is nothing to compare this prediction to.

Level of analysis

There is a good understanding of the experiment, the problems faced with it and are dealt with well. All points of the experiment are explained well and you clearly understand what you are talking about with how you describe it. You have made a prediction, explained it with pre-established facts, then proceeded to make and carry out your experiment with a good choice of apparatus. You have conducted a preliminary experiment and successfully identified any problems, which you have then done your best to eliminate for the final experiment, which shows a good understanding of a good experiment. You end the piece with a decisive conclusion, which you have built up throughout the experiment. You evaluate the experiment and explain any flaws, which shows a good knowledge of the “why” as well as the “what” in the experiment, allowing top marks.

Quality of writing

The piece is overall well communicated, but you do frequently confuse “restrains” with “restraints” and other such errors. These can easily be overlooked though, as your science is solid and these are just minor points. However, proofreading would have caught these and perfected the piece. There are clear, well organized sections so everything is well laid out.

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Reviewed by pratstercs 15/02/2012

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