• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month
Page
  1. 1
    1
  2. 2
    2
  3. 3
    3
  4. 4
    4
  5. 5
    5
  6. 6
    6
  7. 7
    7
  8. 8
    8
  9. 9
    9
  10. 10
    10
  11. 11
    11
  12. 12
    12
  13. 13
    13
  14. 14
    14
  15. 15
    15
  16. 16
    16
  17. 17
    17
  18. 18
    18
  19. 19
    19
  20. 20
    20
  21. 21
    21
  22. 22
    22
  23. 23
    23

Physics - Resistivity

Extracts from this document...

Introduction

image04.pngimage05.png

PHYSICS

AIM

The aim of the experiment I am conducting is to find the resistivity of a 24 watt light bulb. This will be conducted through a series of experiments which will be followed by some calculations using formulas such as:

image06.png

Or

image07.png

ρ is the resistivity (measured in ohm metres, Ω-m)

R is the electrical resistance of the material (measured in ohms,Ω)

image17.pngimage17.png is the length of the piece of material (measured in metres, m)

A is the cross-sectional area of the material (measured in square metres, m²).

There are other equations that could be used to work out electrical resistivity, such as:

image25.png

E is the magnitude of the electric field (measured in volts per metre, V/m);

J is the magnitude of the current density (measured in amperes per square metre, A/m²).

Finally, electrical resistivity is also defined as the inverse of the conductivityσ (sigma), of the material, or:image26.png

Electrical conductivity or is a measure of a material's ability to conduct an electric current. This is because resistivity and conductivity are reciprocals.

I aim to use the first equation to work out resistivity by re-arranging it, like so:

image14.png

So if I can measure ‘R’, being resistance, ‘A’ being cross sectional area and ‘l’ being length of a light bulb, I can use the latter equation to work out the resistivity of the light bulb.

RESISTIVITY

The resistance of a wire depends on quite a few factors; these will affect the wires in many different ways, such as temperature increasing resistance. The length of the wire will make a difference. This is because when you have a long wire, the electrons have to ‘squeeze’

...read more.

Middle


IMPLEMENTING

This is how my final circuit looked; I have included the EMF of the power supply and the power of the lamp in this diagram. image11.png

After conducting my first repeat, I got the following results:

EMF

Voltage across bulb        (V)

Current across bulb        (I)

Resistance of bulb (V/I)

12

10

1.96

5.10

12

9

1.85

4.86

12

8

1.73

4.62

12

7

1.62

4.32

12

6

1.5

4.00

12

5

1.36

3.68

12

4

1.23

3.52

12

3

1.07

2.80

12

2

0.9

2.22

12

1

0.69

1.45

12

0

0


On the second repeat I got the following results:

EMF

Voltage across bulb        (V)

Current across bulb        (I)

Resistance of bulb (V/I)

12

10

1.55

6.45

12

9

1.46

6.16

12

8

1.36

5.88

12

7

1.26

5.56

12

6

1.16

5.17

12

5

1.04

4.81

12

4

0.92

4.35

12

3

0.78

3.85

12

2

0.63

3.17

12

1

0.4

2.5

12

0

0


On the third repeat I got the following results:

EMF

Voltage across bulb        (V)

Current across bulb        (I)

Resistance of bulb (V/I)

12

10

1.55

6.45

12

9

1.45

6.21

12

8

1.38

5.80

12

7

1.28

5.47

12

6

1.18

5.08

12

5

1.06

4.72

12

4

0.94

4.26

12

3

0.82

3.66

12

2

0.66

3.03

12

1

0.51

1.96

12

0

0


On the forth repeat I got the following results:

EMF

Voltage across bulb        (V)

Current across bulb        (I)

Resistance of bulb (V/I)

12

10

1.51

6.62

12

9

1.43

6.29

12

8

1.34

5.97

12

7

1.25

5.60

12

6

1.16

5.17

12

5

1.05

4.76

12

4

0.94

4.26

12

3

0.81

3.70

12

2

0.68

2.94

12

1

0.52

1.92

12

0

0


ANALYSING

So I can see the general trend of my results, and spot any anomalous data, I have drawn a simple I-V graph, which includes all my repeats.

image12.png

As you can see from this graph, my repeats 2 to 4 are very similar but my first repeat isn’t.

...read more.

Conclusion

The actual limitations of my experiment that I couldn’t control were things like, external temperature, obviously the limitations of the equipment I used couldn’t control the environmental temperature around the experiment, so I haven’t taken into account any change in temperature as it is out of my control so I couldn’t do anything about it. Also the accuracy and precision of my voltmeter and ammeter would have an effect on my results, this would cause a systematic error and so my graph’s gradient and thus calculated resistance would still be the same. There could also be random fluctuations in the school’s power supply, or in my power pack, which could result in a temporary random error in my results. I don’t think this happened though, as all my data was very similar, excluding the first repeat. Apart from these factors I think my results are reasonably accurate and precise, they were what I predicted and my 2nd, 3rd and 4th repeats proved to be precise.

I think next time I conduct this experiment; I could do it in a controlled atmosphere, so environmental factors, like temperature and pressure don’t have as much of an effect.

The actual value of resistivity for tungsten is  0.0000000528 Ωm at room temperature. The value I got for this according to my results is: 0.0000054 Ωm. This difference would be because of the level of control and accuracy that I had over my equipment and environment. I think that to do this experiment and get the results nearer the standard value of resistivity for tungsten I would need to have this control over the environment, I would need to do more repeats, I would need to take a lot of other factors into account and I would need to use expensive voltmeters and ammeters, that will provide a better accuracy and precision.

...read more.

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Electrical & Thermal Physics essays

  1. In this experiment, we will measure the e.m.f. and the internal resistance of a ...

    Besides, the connecting wires used in the experiment are ideal wires with no resistance; it will cause inaccurate readings of both ammeter and voltmeter. Each wire has its own resistance and then most of them are connected in series circuit.

  2. The potato - a source of EMF

    Or in my words, the Maximum Power output can be achieved from the potato cell to the load can be achieved when the internal resistance is equal to the load resistance. By observing what values of resistance the peaks of the curves are I can then see if it matches

  1. Finding the Resistivity of a Wire

    At each point I will measure the diameter twice, with readings at 90� angles to each other to ensure that the wire is cylindrical. o Voltage across length of wire: measured using voltmeter at 10 different lengths of wire - from 1.00m to 0.10m at 0.10m intervals, each repeated three times.

  2. I am going to investigate what the resistivity is of a pencil lead. ...

    I will try to make it as accurate as possible by using an electric ammeter and a voltmeter where the intervals are 0.1V. Preliminary Experiment I will be carrying out a preliminary experiment so that I know exactly what I am doing and can eliminate any problems that I may come across.

  1. Investigating the effect of 'length' on the resistance of a wire

    Some conductors are better than others. For example, copper is a better conductor than iron. When the electrons are moving through the metal structure they bump or 'collide' into the metal ions and this causes resistance to the electron flow or current.

  2. Investigation On The Resistivity Of Apples. Since we are measuring the resistance of an ...

    Cut another 1 x 1 x 1 cm slice of apple and immediately measure the resistance three times again. 4. Repeat step 2 until three slices of apple of the same length have been measure for its resistance three times each. 5. Record the values in a table. 6.

  1. Investigation into the resistance of a filament lamp.

    Many different types of radiation have been identified. Each of these types is defined by its wavelength. The wavelength of electromagnetic radiation can vary from being infinitely short to infinitely long It's pretty hard to accurately measure the wavelength of light. The problem is that the wavelengths are very small.

  2. Does the length of a conduction putty affect its resistance?

    The list below shows all the controlled variables in my experiment: 1. Before I turn on the mains, I will make sure that my hands are completely dry, in order to avoid the risk of electrocution.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work