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Resistance of a wire.

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Physics coursework

Resistance of a wire

The resistance of a wire depends on a number of factors:

1: The length of the wire
2: The temperature of the wire

3: The material the wire is made out of
4: The cross sectional area of the wire

In this investigation I am going to look at the effects that changing the cross sectional area of a nicrome wire has on the resistance of the wire.


I predict that as the cross sectional area of the wire increases the resistance will decrease,

this can be called Inversely proportional. I think this because for each of the 4 factors

above there is a scientific reason. I have stated all 4 just for demonstrational purposes

but I am specifically looking at number 4.

1: As the length of the wire increases the resistance increases. This factor is known as a

proportional factor because it makes the result of the experiment increase as it increases its self. Proportional factors are demonstrated in graph Aimage00.png

2: As the temperature of the wire increases

the resistance also increases, this is another

example of proportional factors.

3: each different type of metal has a

different resistance which depends

on the properties of the metal.                          

                                                                   Graph A

4: As the cross sectional area of the wire increases the resistance of the wire decreases.

...read more.



circuit to take readings of the current and the

voltage, from these I can work out the

resistance using the equation R = V / I which

stands for Resistance= Voltage  / Current.

The circuit I set up is shown is the diagram

To the right:

The Ammeter, represented by the A in a circle,

measures the current in the circuit in amps and must be placed in series to work. The voltmeter, represented by the V in the circle, measures the voltage in the circuit in volts and must be placed in parallel to function correctly. I then will do all the experiments using the same equipment so that it will be a fair test. For safety reasons I will not let the current in the circuit pass above 3amps. Before I start my

experiment I will do a preliminary experiment to make sure everything is working correctly, if any

alterations need to be made to the circuit or any other part of the experiment I will make them. The purpose of this preliminary experiment is so that I do not run into any problems while I am doing the experiment as I do not want to change anything while I am do it as I want to minimise experimental error.

Preliminary Experiment

...read more.


I didn’t make any improvements from the preliminary experiment to the real experiment, this was because my preliminary experiment was a complete success. The conclusions that were made were correct. I can tell this because it is supported by both my experimental evidence and my theoretical evidence.

I could have undertaken this experiment in a different way. Instead of using a voltmeter and an ammeter and taking readings from both at different set currents and then using them to work out the resistance; I could have used an ohmmeter and a voltmeter then taken the resistances at different set voltages. I could do this to extend and expand my experiment and look deeper into the formulae and rules to see if I could find any flaws in them. I could also do number of other things to expand my experiment:

  1. Change the material of the wire. This could test the formula Resistance =

(Resistivity X length) / Cross sectional area. It would also verify my main prediction and conclusion that resistance is proportion to cross sectional area. Using different materials would also tell me how conductive a type of material is relative to another type of material.

  1. Change the length of the wire, this would lead me to testing the theory of proportionality between length and resistance. This would be a very suitable and good extension to my investigation.

...read more.

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