# Find the resistivity of nichrome.

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Introduction

## An experiment to find the resistivity of nichrome

A. Planning

Plan of the method to be used: -

The resistivity of nichrome can be determined using the equation ??=?RA/L

Where:

R:- Is the resistance of the wire in ?"ohms" and can be determined using the equation R=V/I where "V" is voltage in volts and "I" is current in

amperes.

L:- Is the length of the nichrome wire used in metres.

A:- Is the cross-sectional area of the wire in metres square and can be determined using the equation A= ??d2 where "d" is the diameter of the wire.

If I plot a graph of length on the x-axis against resistance on the y-axis. From the relation R = ? L /A which corresponds to the st. line equation ?

y=mx the graph should be a st. line passing through the origin where "m" is the gradient of the st. line graph and corresponds to ?/A. Since the cross-sectional area of the wire can be found by knowing it’s diameter. Therefore the resistivity of nichrome can be calculated.

Middle

chosen are as follows : 20cm , 40cm , 60cm , 80cm and 100cm. I have chosen these lengths because

they are easily measured by the meter ruler and give a good range.

Below is a circuit diagram of the circuit I am going to use in my main experiment:

POWER SUPPLY

2 VOLTS

AMMETER

VOLTMETER

CROCODILE CLIPS

WIRE

METER RULER

In my main experiment instead of using an ohmmeter I have chosen to use an ammeter and voltmeter ,

I have done this so that instead of relying on the ohmmeter to give the resistance I will calculate the

resistance of the wire , I shall calculate the resistance of the wire using the equation below.

RESISTANCE = VOLTS

AMPS

I have chosen to use a meter ruler because the lengths that I will be measuring are to big for a smaller

ruler and also the meter ruler can be accurate to +1mm or ¡V1mm.

Results

SWG

(thickness/mm)

Conclusion

From my graph, I can see that my results were accurate. All the points are very close or on the line of best fit in a positive correlation. There were no anomalous results.

As I obtained accurate results, I think that the method I used was suitable.

However, there are certain improvements I could make to improve the accuracy, namely:

· Making sure the wire is straight so measurements could be taken accurately.

· Making the wire straight would enable more accurate positioning of the crocodile clips, which again would give more accurate results.

· Letting the wire cool down sufficiently in between readings. When the wire heats up, it has lots of energy, which causes the atoms in it to vibrate, making it harder for the electrons to travel. This increases the resistance via another method, so it is not a truly fair test.

As I have previously stated, my results have a good standard of accuracy. This is shown by the points being near or on the line of best fit and there were no anomalous results. Therefore my results support a firm conclusion that the length of wire is proportional to the resistance.

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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