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# What factors effect the electrical resistance of a wire?

Extracts from this document...

Introduction

Physics Coursework for G.C.S.E.

"What factors effect the electrical resistance of a wire?"

Background Knowledge and Hypotheses

Resistance - This is the force that resists the flow of electrical current                                running through any material (this will vary from one                              substance to another, also from 'Conductor' to 'Insulator'.)

In this investigation it is the resistance of the conductor that we will be                                                             measuring,

i.e. Metal wires which will be looked at. (Examples of materials include : Steel, Nichrome (Nickel and Chromium alloy) and Copper.)

The (electrical) resistance can be measured by Ohm's law :

V  =  I     R

Voltage/ Potential DifferenceCurrentResistance

(Energy given to push the               (The flow of electrons.)        Measured in Ohms/ R.

electrons around an circuit.)              Measured in Amps/ I.

Measured in Volts/ V.

If this equation is rearranged, then:

R =    V

I

i.e. if the voltage/ potential difference across the material is measured,    along with the current, then the resistance can be calculated.

N.B.

Metals according to their structures can be either 'good' conductors or 'bad' conductors. This depends on the element/ alloy and therefore how the atoms/ particles are arranged in the solid form.

The diagram below illustrates the structure of a typical metal.

COPPER (Metals have Crystal/ Lattice structures)

Copper (positive) ions

Electrons from outer shell, free to move in any dimension, therefore metals conduct heat and electricity.

Middle

Here the wires have to be the same thickness, otherwise more than 1 variable will be experimented with and therefore make it a unfair test.

(N.B. Also for each of these two hypothesis the materials of the wire(s) must be the same, again to perform a fair test.)

3.The Temperature of the wire

According to theory (ref. Advanced 'A' level physics), metals conduct better when at low temperatures and poorly at high temperatures. This is because, at a low temperature the atoms/ particles within a wire are hardly moving, therefore do not block the flow of electrons (and these are the charge carriers), but as the temperature increases, the particles have increasing Kinetic Energy and therefore are vibrating increasingly faster, hence will steadily 'block' the flow of electrons through the wire, so resistance of the wire also steadily increases. On this basis, I would expect an inverse relationship between R (resistance) and T (temperature).

i.e.               R                    I

T

The only problem I can anticipate here looking at this prediction is how to control the temperature, because when wires have 'higher' resistance's they become hotter anyway, therefore the control of the temperature might become difficult, so maybe only qualitative,

i.e. Generalised results might be obtained

Another difficulty is that, if that this relationship is true, the metal wire might melt before you reached the temperature required for the result needed.

Conclusion

There are several areas which in theory I could extend this investigation if I had another opportunity to do it.

e.g. I could see what happens if the two variables, i.e. length and cross-sectional area are varied at the same time. I suspect that probably the two relationships could be expressed in an overall equation, namely,

R            L

A

Also, clearly different materials will have different resistance values, because they have slightly different structures.

i.e. Some materials will be poorer resistors and others will be better resistors. So the same hypothesis tests could be carried out on other materials.

Also initially I thought about testing out the temperature of the material as a variable, but having done a trial experiment, I found this was a waste of time, because there was no accurate way in which I could record the temperature of the wire.

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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