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An investigation into how the resistance of wire is related to the length.

Extracts from this document...

Introduction


BACKGROUND INFORMATION

A circuit is a continuous path, which is composed of an electromotive force (a power supply/battery) to drive the current around the circuit and conductors and conducting devices to carry the current, in a full circuit.  In a circuit, the direction of flow is always from the positive side of the battery to the negative side (this is a conventional flow), but the electrons flow in the opposite direction as they are negative and so they are attracted to the positive side.  This is called a closed circuit.  A series circuit is where the current is passed through every device which is part of the circuit without branching off into parallel circuits.

Metals conduct electricity.  This is because of their structure – a regular lattice arrangement of charged ions which are surrounded by electrons.  Metals are good conductors of electricity because the electrons are free to move inside of the metal.  This is because the electrons can easily detach themselves from their atom.

image00.png

In an atom, the majority of the mass is contained in the nucleus.  The nucelus consists of protons and neutrons.

PARTICLE

MASS

CHARGE

proton

1

+1

neutron

1

0

electron

1/1870

-1

The electrons in the atom orbit the nucleus, similar to the planets orbiting the sun.image01.png

...read more.

Middle

2.3

0.1739

5

0.3

2.3

0.1304

10

0.2

2.4

0.0833

10

0.2

2.4

0.0833

10

0.2

2.4

0.0833

15

0.2

2.4

0.0833

15

0.2

2.4

0.0833

15

0.2

2.4

0.0833

CONCLUSION

These experiments did not work, as all of my results are roughly the same.  This is because the resistance was too low in the wire to see a noticeable change in the meter readings.  As nickel chrome is a fairly thick wire I have decided to proceed with the rest of my experiments using a wire which has a higher resistance, so a smaller cross sectional area.  The wire I chose was constantan wire.


HYPOTHESIS

I predict that when using a thinner wire I will obtain good results and that I will be able to show clearly the increase of resistance as I increase the length.  This will be because the amount of atoms in the wire has increased and so there will be more atoms to collide with the electrons.  

I think that when I plot a graph of unit length (cm) against resistance (ohms) it will show clearly that they are proportional to each other, as I think when the length of the wire is doubled, the resistance will be too. I think that the graph will look similar to:

image02.png

...read more.

Conclusion

5.1 - 5.23 = -0.13

-0.13/5.1 = -0.0255 (to 3 significant figures)

-0.0255 x 100 = -2.6% (to 1 decimal place)

These accuracy problems could be due to parallax error (I could have looked at the metres from different angles each time), temperature changes due to the wire getting heated or the variation in the contact made by the crocodile clips.

EVALUATION

I feel my overall results were accurate.  This is shown in my graph where the points I have plotted are touching or very near the line of best fit.  I did not have any anomalous results; the reliability of my results was increased because I conducted 3 experiments at each length.  

I found it quite difficult measuring the wire accurately.  This is because it was hard holding the wire straight while measuring it and then using the crocodile clips to secure the length.  I was not sure that the crocodile clips were very secure, but by looking at my graph I now think the lengths I measured were accurate and the connections secure enough.  

If I were to redo my experiments I would change the following factors: I would use pointers instead of crocodile clips, as they are more accurate because they have a smaller tip and they would not constrict the wire where they were attached to it.  I would also prefer it if the wire were completely straight before I start my experiments.


BIBLIOGRAPHY

Oxford Interactive Encyclopedia                        CD – ROM

AirCom Education                                        CD – ROM

Physics For All                                        Book

Radio Communication Handbook                        Book by RSGB

...read more.

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