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# Resistance of a Wire Investigation

Extracts from this document...

Introduction

## Aim

The aim of this investigation is to find out how changing the length of a piece of wire will affect its resistance.

Prediction

I think that increasing the length of a wire will increase its resistance. This is because in a conductive metal, the electrons in the outer shell of each atom are free to move around. An electrical current is where all these electrons are caused to move in the same direction through the metal. Resistance is the property of a substance that restricts the flow of electricity through it, and is often associated with heat. As the electrons are passing through the metal, they are constantly colliding with the atoms of the metal, causing their course to be slowed down. The collisions cause changes of direction which dissipate energy as heat, which is why more resistant metals heat up more than metals which let electrons pass through more easily. It is easier for electrons to pass through metals in which the atoms are small and far apart, because the free electrons can pass through with less collision to slow their path. It is most important for the metal to contain a lot of free electrons. Fewer collisions mean that less energy is transferred to heat: this is low resistance. As the length of the wire is increased, there will be more fixed atoms for the free electrons to collide with, thus slowing their course.

The length of the wire and the resistance of the wire will be directly proportional. If you double the length of the wire, the resistance will also double. This is because there will be double the amount of atoms in the wire for the electrons to collide with.

...read more.

Middle

4.03

0.32

45

4.07

0.29

50

4.11

0.26

55

4.14

0.24

60

4.17

0.22

It is clear to see here that nichrome will be suitable for the experiment. Neither voltage nor amperage gives any very extreme readings, and it is possible to use sensible lengths of wire and get a lot of results.

Results

The first experiment

 Length of nichrome wire(cm) Voltage(V) Current(I) in amps (A) 5 0.3 0.6 10 0.45 0.53 15 0.3 0.22 20 0.35 0.21 25 0.4 0.19 30 0.42 0.18 35 ---------------------------- ---------------------------* 40 0.46 0.15 45 0.45 0.13 50 0.5 0.12 55 0.5 0.12 60 0.5 0.11 65 0.6 0.12 70 0.7 0.13

The experiment repeated

 Length of nichrome wire(cm) Voltage(V) Current(I) in amps (A) 5 0.3 0.75 10 0.4 0.64 15 0.6 0.56 20 0.75 0.51 25 0.82 0.45 30 0.9 0.42 35 ---------------------------- ---------------------------* 40 1 0.35 45 0.57 0.16 50 0.46 0.17 55 0.5 0.15 60 0.55 0.16 65 0.59 0.15 70 0.6 0.14

Processing the results

Resistance and averages of both tests:

 Experiment 1 Experiment 2 Average resistance (Ω) Length Resistance(Ω) Resistance(Ω) 5 0.5 0.4 0.45 10 0.85 0.63 0.74 15 1.36 1.07 1.22 20 1.67 1.47 1.57 25 2.11 1.82 1.97 30 2.3 2.14 2.24 35 ---------------- ---------------- ---------------- 40 3.07 2.86 2.97 45 3.46 3.56 3.51 50 4.17 2.71 3.44 55 4.17 3.3 3.75 60 4.55 3.44 4 65 5 3.93 4.47 70 5.38 4.29 4.84

The cross-sectional area of each wire is:

πr2 =πx (0.2285/2)2   = 0.041mm2 (3 s.f.)

Conclusion

If the length of a piece of nichrome wire is increased, its resistance increases. You can see in my graph that as I predicted, the two look directly proportional: The two increase at the same speed, and at a constant rate.

...read more.

Conclusion

Another problem that should have been more carefully tackled was that of the two lesson break. If I had thought ahead, I would have recorded what equipment we used so that we could use the same again. If I had done so, it would have made it easier to prevent the anomalies at 45cm and 50cm.

Improvements – additional evidence

There are many ways in which I would have liked to provide more evidence. It would have been a good idea to do the original experiment three times, because that way, if one set of results was wrong, it would be easier to tell as it would stick out as being different.

I would have liked to repeat the experiment with different metals: to see how they vary, and to check that my prediction is correct for more metals than just nichrome. It cannot be taken for granted that all metals will behave the same as nichrome has done. I would probably use copper and constantan in the same circuit as I used for nichrome. Because I would be changing the metal, I would have to keep all the other variables the same as they were before, and take the same fair-testing precautions. I would not use quite so many different lengths of wire as I did when testing nichrome because all I would want to discover from this experiment was that the trend I found in nichrome is true for all metals. I would expect it to be true, as there is strong scientific proof behind it, which I have explained fully in my prediction: All conductive metals share a similar structure, and their free electrons behave in the same way, so it follows that they should behave the same.

...read more.

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