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# The aim of this course work is to calculate a value for the resistivity of a certain wire. This will include an experiment and a write up. I have done the first part of the write up which includes the plan and the method before the doing the experiment.

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Introduction

## RESISTANCE AND RESISTIVITY

The aim of this course work is to calculate a value for the resistivity of a certain wire. This will include an experiment and a write up. I have done the first part of the write up which includes the plan and the method before the doing the experiment. The rest of the write up will be done after the experiment. I will be using a 24SWG constantan wire for this coursework.

WHAT IS RESISTIVITY?

The resistance of a conductor depends on the material it is made of as well as its dimensions. This resisting property of a material is called its resistivity and is given the symbol ρ (Greek letter ‘roh’). Conductors and resistors have resistances; the materials of which they are made have a resistivity. When the resistivities of different materials are compared; we actually compare the resistances of conductors made from a standard size specimen of the materials. This gives the definition of resistivity:

The resistivity of a material is numerically equal to the resistance of a specimen of unit length and unit cross-sectional area

To calculate the resistivity of the wire I will need the following:

1. The resistance of the wire at different lengths.
2. The cross sectional area of the wire in m2.

FINDING THE RESISTANCE OF THE WIRE AT DIFFERENT LENGTHS:

I can work out the resistance of the wire by measuring the current through it and the voltage across it.

Middle

1.9

2.8

R

2.157

2.000

2.000

1.929

2.021

0.9

V

1.1

2.3

3.7

5.3

Average R in Ohms

I

0.6

1.3

2.1

3

R

1.833

1.769

1.762

1.767

1.783

0.8

V

1

2.3

3.6

5.2

Average R in Ohms

I

0.6

1.4

2.3

3.4

R

1.667

1.643

1.565

1.529

1.601

0.7

V

1

2.2

3.5

5

Average R in Ohms

I

0.64

1.6

2.5

3.7

R

1.563

1.375

1.400

1.351

1.422

0.6

V

0.9

2.1

3.3

4.8

Average R in Ohms

I

0.74

1.7

2.8

4.2

R

1.216

1.235

1.179

1.143

1.193

0.5

V

0.8

2

3.2

4.6

Average R in Ohms

I

0.88

2.1

3.3

4.8

R

0.909

0.952

0.970

0.958

0.947

0.45

V

0.8

1.9

3

4.4

Average R

Conclusion

By this experiment I have reached the conclusion that resistance is proportional to the length of the wire taking experimental errors into account.

Using the above graph I calculated the average resistance for 1 unit length (which is 1 metre). I did this by finding the gradient of the straight line on the graph.

Resistance of 1 metre of the wire = 1.971 Ω

As this is an average from a lot of values the accuracy is increased to ±0.005 Ohms.

The main aim of this experiment was to find the resistivity of the wire. To find the resistivity of the wire I have to use the formula:

The data I need to work out the resistivity is:

• A length of wire and its resistance: I have got these values from the above experiment and calculations.
• The cross sectional areas of the wire.

I had to work out the cross sectional area of the wire. I measured the diameter of the wire ‘’ using a micrometer. To increase accuracy I took 3 readings from different places on the wire and took an average of the three as my measurement.

= metres.

A=            A=

The cross sectional area of the wire (to 5 s.f.) = A = 2.4630*10-7 m2

Data:             = 1.00 m                    R   = 1.971 Ω           A = 2.4630*10-7 m2

= =  4.855*10-7Ωm (to 4 s.f)

RESISTIVITY of 24swg consantan wire =

4.855*10-7Ωm (to 4 s.f)

Physics experiment write-up by Sarwar Akeel Akbar –6M

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