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Investgating resistivity - Planning and Implementing

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Introduction

Physics Coursework – Planning and Implementing

This investigation aims to test the relationships within the formula R= ρl/A, resistance in ohms equals resistivity in ohm metres multiplied by length divided into cross-sectional area, and to find a value for the resistivity of constanton (how strongly constanton opposes the flow of an electrical current), ρ.

I aim to find two values for ρ, one to be obtained through an experiment, and the other to be obtained using data books. By obtaining and comparing these two values, I hope to find a reliable and realistic value for constanton’s resistivity.

Plan of Investigation

Apparatus List

Just over a metre length of constanton wire, between 0.2mm and 0.4mm in diameter, to be attached using sellotape to a metre rule, calibrated in mm.image00.png

Variable resistor, 0-12Ω

Digital Ammeter, 0-10 A, +/- 0.005 A

Digital Voltmeter, 0-20 V, +/- 0.005V

Leads

Pair of crocodile clips

Micrometer

Power pack, supplying 0-2 V, direct current

The experiment - Plan

First, the metre of constanton wire must be straightened to allow it to be measured accurately. The diameter of this wire should then be measured, using the micrometer. (The zero error of the micrometer must be measured first, to ensure that the value for the diameter is as accurate as possible). Measure the diameter in three places, then compare these results. If they are not equal (to within experimental error)

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Middle

  Using the same wire for each length will also ensure that ρ remains constant as well.

Implementing

Precision of readings

The voltmeter and ammeter measure to the nearest 0.005, hence all values for voltage and current are recorded to two decimal places. Resistances are also given to two decimal places, as given the accuracy of the voltage and current the resistance is calculated with, further decimal places could not be supported. Length is measured to the nearest mm, so these values in metres are given to three decimal places. Diameter is measured to the nearest 0.005 mm, so it is given in millimetres to two decimal places.

Significant sources of error

The length of wire, current and voltage, and the wire’s diameter are measured. The length of the wire has the smallest error, as the smallest value is 0.1m, and it is measured to the nearest millimetre. Percentage error, at its highest, was therefore

image01.png

0.5% was not a particularly significant error, especially given this error only occurs once, at 10cm, and the other errors at greater lengths are smaller.

For voltage and current, the maximum error is of 0.005 when the voltage or current is at its lowest. For voltage the highest percentage error was therefore

image02.png

And for current the highest percentage error was therefore

image03.png

These errors are quite significant.

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Conclusion

>0.32

7.06

7.04

0.700

3.17

0.52

6.10

2.56

0.42

6.10

1.82

0.30

6.07

6.09

0.600

2.94

0.56

5.25

2.14

0.41

5.22

1.52

0.29

5.24

5.24

0.500

2.86

0.66

4.33

1.08

0.25

4.32

0.92

0.21

4.38

4.34

0.400

1.01

0.29

3.48

0.78

0.22

3.55

0.70

0.20

3.50

3.51

0.300

0.91

0.35

2.60

0.77

0.29

2.66

0.55

0.21

2.62

2.62

0.200

0.69

0.39

1.77

0.46

0.26

1.77

0.36

0.21

1.71

1.75

0.100

0.44

0.51

0.86

0.23

0.26

0.88

0.32

0.36

0.89

0.88

First Attempt

Second Attempt

Third Attempt

Mean diameter

Wire diameter/mm

0.25

0.25

0.25

0.25

Kathleen Emerson                Page

Durham High School for Girls

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4 star(s)

Response to the question

Response to question:
The candidate has responded extremely well to the question. In the beginning of the coursework he has clearly stated out what he aims to do and how he wants to do it. However he has not compared ...

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Response to the question

Response to question:
The candidate has responded extremely well to the question. In the beginning of the coursework he has clearly stated out what he aims to do and how he wants to do it. However he has not compared the calculated value of constanton's resistivity with the one from the data booklets like he stated he would. This piece of work, overall includes every detail need at GCSE level to perform this experiment.

Level of analysis

Level of analysis and accuracy:
The candidate has a very good level of analysis. He shows clear understanding as to how the data collected can be used to calculate the value of rho. The candidate shows high level of accuracy by referring to uncertainties of instruments and how to overcome them. However there is one flaw. The author has tabulated the results obtained from the experiment but he has not plotted a graph and calculated the gradient. He has also not stated the calculated value of the resistivity of constanton.

Quality of writing

Quality of writing:
The quality of writing is very good. There are no significant grammatical errors. The candidate has written the coursework in a very planned and organized manner. There is a clearly labelled diagram with all the instruments used listed along with their ranges. The procedure followed is clearly stated. Overall it is very insightful and easy to understand.


General notes:
In order to minimize the temperature increase in the wire, the candidate has suggested using a low current, however overheating of wire would more effectively be minimized if the system is allowed to cool before each time the power pack is switched on.

In a nutshell, this is an extremely good course fit even for A-level.


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Reviewed by shreyasi.hait 01/03/2012

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