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Resistivity of a Wire

Extracts from this document...

Introduction

Resistivity of a Wire

Aim:

The aim of this investigation is to see how the length of Nichrome wire affects its resistance

Pre-test Results:

 Wire Type Swags Length of Wire(cm) Voltage(v) Current(a) Resistance(Ω) Constantan 26 102040 13.527.556.4 0.4 37.5687.51410 Copper 26 102040 0.91.52.5 0.4 22.537.562.5 Nichrome 26 102040 32.559.4118.3 0.4 812.514852957.5

Pre-test Findings:

From my pre-test, I found out that using the nichrome wire would be best to use because it gave the both more reliable results and were also closer together. Constantan was not suitable for the investigation because it gave very inaccurate results- the range was very large. Copper was not suitable both because it had a very low resistance, and also heated up very fast, so could burn someone. Therefore I decided to use nichrome wire.

I also decided to use a wooden block to keep hold of the wire, because it will keep the wire taut and also to prevent anyone getting burnt.

Another thing I decided was to use digital multimeters because they give more accurate results- to 2dp- and can measure both the current and voltage on the same instrument.

The ranges of lengths I will be using for my final investigation are: 0.2m, 0.4m, 0.6m, 0.8m and 1.0m.

Fair Testing:

Middle

0.000000159

0.2m = 0.2 x (110 x 10-8) ÷ 0.000000159 = 1.38 Ω

0.4m = 0.4 x (110 x 10-8) ÷ 0.000000159 = 2.77 Ω

0.6m = 0.6 x (110 x 10-8) ÷ 0.000000159 = 4.15 Ω

0.8m = 0.8 x (110 x 10-8) ÷ 0.000000159 = 5.53 Ω

1.0m = 1.0 x (110 x 10-8) ÷ 0.000000159 = 6.92 Ω

Prediction Continued:

I also predict that the resistance is directly proportionate to the length of the wire. If you double the length of nichrome wire, so will the resistance. From my predicted results, I can see that when I double the length from 0.2m to 0.4m, the resistance almost doubles too, from 1.38Ω to 2.77Ω. In the same way, if I triple the length of wore from 0.2m to 0.6m, the resistance is once again almost triple, from 1.38Ω to 4.15Ω. This also works if I quadruple the length of the wire from 0.2m to 0.8m and if I increase the length of wore 5 times, the resistance also increases in the same way. This can be seen not only when using 0.2m of wore but also if I double the length of wore from 0.4m to 0.8m, the resistance is almost double too, from 2.77Ω to 5.53Ω. This is because there is 2, 3, 4, or 5 times the length of wore, which means that there will also be 2, 3, 4, or 5 times more nichrome atoms present in

Conclusion

In order for the investigation to be fairer, I think the temperature of the wire should have been kept constant. This had an effect on the investigation, because from my research, I found out that another factor affecting the resistance in a wire was the temperature too. As the temperature of the wire increased, so did the resistance. This is because as the wire gets heated, the particles gain kinetic energy, therefore making the flow electrons harder. This makes the particles move around more, therefore colliding with the electrons, and blocking their way, and taking longer for the electrons to move to the other side of the wire. This results in an increase of resistance.

It would be very difficult for the temperature of the wire to be kept constant. A water-bath would not be suitable because there would be a potential health hazard, as water is an excellent conductor of electricity.

There is however a device known as a thermocouple, which can help us check the temperature is at a constant level or not. How it works is that it is connected in the circuit. They work in the sense that if the temperature of the wire goes above a given temperature, the thermocouple stop working, therefore breaking the circuit and so will not work.

Zoya Khan         1354        13228

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