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# investigating the relationship between the diameter and the current in a wire at its melting point

Extracts from this document...

Introduction

Investigation Report

Aim

Theory

Electrical resistance is a measure of the degree to which an object opposes the passage of an electric current. The SI unit of electrical resistance is the ohm. Its reciprocal quantity is electrical conductance measured in siemens.

Resistance is the property of any object or substance of resisting or opposing the flow of an electrical current. The quantity of resistance in an electric circuit determines the amount of current flowing in the circuit for any given voltage applied to the circuit.

Some formulae for resistance are

where

R is the resistance of the object / Ω

V is the potential difference across the object / V

I is the current passing through the object / A

(Ref. http://en.wikipedia.org/wiki/Electrical_resistance)

where

Middle

wires()Voltmeter(V)Ammeter(A)Variable resisterPower supply

Result

 SWG d/mm Voltage/V 14 0.195 0.199 0.196 0.002 0.005 0.008 0.01 16 1.11 1.03 1.06 0.024 0.046 0.067 0.089 18 0.12 0.199 0.122 0.005 0.01 0.02 0.03 20 0.95 0.91 0.96 0.008 0.016 0.024 0.031 22 0.76 0.73 0.76 0.013 0.026 0.04 0.052 24 0.055 0.055 0.056 0.538 1.03 1.56 2.07 29 0.033 0.032 0.032 2.63 5.03 7.51 10.14 35 0.027 0.027 0.026 4.93 10.22 14.85 19.88
 SWG Current/A Resistance/Ω 14 0.251 0.502 0.751 1.003 0.007968 0.00996 0.010653 0.009973 16 0.254 0.5 0.728 1.009 0.094488 0.092 0.092033 0.088206 18 0.254 0.506 1.001 1.501 0.019685 0.019763 0.019987 0.02008 20 0.246 0.503 0.756 1.003 0.03252 0.031809 0.031746 0.030907 22 0.252 0.501 0.757 1.003 0.051587 0.051896 0.05284 0.051845 24 0.255 0.497 0.753 1.003 2.109804 2.072435 2.071713 2.063809 29 0.246 0.494 0.75 1.003 10.69106 10.18219 10.01333 10.10967 35 0.248 0.501 0.754 1.005 19.87903 20.3992 19.69496 19.7811
 SWG Range in d

Conclusion

The gradient of the line should be .

= 0.621Ωm

 SWG R 1/d^-2 y = mx + c % difference between data point and best fit line 14 0.009638 25.85 -0.2078 -105 16 0.09168 0.8789 -0.5410 -117 18 0.01985 46.28 0.06466 -69 20 0.03175 1.132 -0.5376 -106 22 0.05204 1.778 -0.5290 -110 24 2.079 326.6 3.804 -45 28 10.249 956.5 12.21 -16 32 19.94 1406 18.21 10

The worst case difference between the data point and the best fit line is -117%.

## Evaluation

The % uncertainty in R should be about ±14% according to the calculation. However, the worse difference is –117%.

Sources of error:

1. 1% error during the measurement of length of wire.
2. 27% error during the measurement of diameter of wire.
3. 14% error when reading the ammeter and voltage.

Improvement to the method:

1. Use longer wires.
2. Measure the thickness of the wire at as many places as possible.
3. Use as many significance as the ammeter and voltmeter can use.

The final uncertainty for the experiment is 100%.

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

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## Here's what a star student thought of this essay

4 star(s)

### Response to the question

This is a good report but a lack of conclusion and some significant errors in analysis of uncertainties have let it down somewhat.
The writer initially makes clear what the task is and how they approach it. The explanation of ...

### Response to the question

This is a good report but a lack of conclusion and some significant errors in analysis of uncertainties have let it down somewhat.
The writer initially makes clear what the task is and how they approach it. The explanation of the equations are good but the full derivation and rearrangement isn't required in this type of report. For a final report, the full results before averages are taken should be relegated to an appendix. The biggest problem is that the results are actually OK and the final graph reasonable. The actual uncertainty is approximately 10% rather than the 100% quoted. This can be determined from your graphing software, which usually has a value for this.

### Level of analysis

The physical concepts aren't discussed in particular detail but it is largely accurate, with some relevant physics discussed.

### Quality of writing

The layout is good with good spelling, punctuation and grammar in general. The appropriate scientific terms are spelt correctly.
Overall, a good report with some room for improvement.

Reviewed by k9markiii 08/03/2012

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