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# The resistance of a wire

Extracts from this document...

Introduction

## Tommy Clifford 10D

Physics-Coursework (Practical)

## Background

In a metal, the atoms exist as positive ions surrounded by electrons, some of which are free to move within the crystal structure.  At all temperatures above absolute zero, all the particles are in constant motion. The ions held in place by strong binding forces, simply vibrate in their fixed positions, while those electrons that are free can move about place to place.  Without an external electric field, the electrons rapidly and randomly move about in all directions.  There is no net motion in any particular direction. This is illustrated in the diagram.

By connecting a battery, all the charged bodies (the positive nuclei, orbital electrons and free electrons) experience a force.  The positive nuclei are more attracted towards the more negative potential, while the electrons are attracted towards the more positive potential.  However, only the free electrons can move under the actions of this force.  This force will accelerate these electrons, but their speed is limited by collisions with the metal ions.

Middle

Resistance is the opposition in the current of the flow.

R = P1/A

Where R = resistance

1 = length

A = cross-sectional area

P = Resistance

R is directly proportional to 1.

The resistance increases as the length of the wire increases because the voltage down the wire pushes the electrons; the atoms however vibrate up

## Tommy Clifford 10D

and down making it difficult for the electrons to pass. Therefore the longer a piece of wire is the more resistance there is (see diagram below).

Apparatus

The apparatus that I will be using for this experiment is as follows;

• Crocodile clips,
• Voltmeter
• Ammeter
• Rheostat

Plan

1. Using crocodile clips the wire will be connected to the voltmeter, ammeter and rheostat as in the diagram
2. Both the rheostat and the ammeter will the n be connected to the energy source but the energy source will not be turned on.
3. The crocodile clips be placed 10cm apart from each other.
4. The energy source will be turned on

Conclusion

For this experiment each reading will be repeated 3 times to provide an average.  This will provide valuable data for the later part of the investigation.

## Tommy Clifford 10D

Evaluation

If I did the experiment again, I would use not only the length but the cross-sectional area to measure the resistance as well.  I would then repeat the experiment with different wires of different cross-sectional areas. This would ensure an even more accurate result.

One thing that went wrong in my experiment, was that I did not put the voltmeter in parallel to the circuit at first, so I got completely wrong results and had to carry out the experiment again.

Conclusion

With reference to the graph, there is a positive correlation.  This proves my hypothesis to be correct. If you increase the length the resistance will also increase i.e. if you double the length of the wire, the resistance will double also.

In conclusion I think that my experiment went very well and I gained a fair result out of it.

This student written piece of work is one of many that can be found in our GCSE Electricity and Magnetism section.

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