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# Physic's Investigation into the resistance of a brine soaked piece of paper, related to its surface area

Extracts from this document...

Introduction

Physic’s Investigation into the resistance of a brine soaked piece of paper, related to its surface area

Aim                I aim to discover how length and cross-sectional area affect the resistance of brine soaked chromatography paper when an electrical current is passed through it.

Predictions

• Firstly I think that as the length decreases the resistance will decrease proportional.
• Resistance is when current is slowed; this happens by the moving electrons (current) colliding with each other or any molecules and atoms they pass through.  Through this the electrons lose some of their kinetic energy which changes into heat energy and thus resistance is created and the current slows.
• My previous prediction is based on this theory. It is due to the fact that the shorter length of brine soaked paper, the less distance the current has to travel. This means that the free electrons have less distance and thus time to collide with each other and any other molecules (from the paper, and NaCl solution).  Further more, if I were to double the length of paper then I believe the resistance would also double.  This is because twice as much of the brine soaked paper means that there is twice as many molecules for the electrons to collide with, and twice the distance to travel.
• Secondly I predict that as the cross-sectional surface area decreases the resistance will increase
• This is because, as the width of the paper decreases there is less room for the flowing electrons. They are therefore more likely to collide with one another and other molecules. The resistance will thus increase, as the same voltage is trying to get through a smaller area.

Middle

1

2.91

2.91

2.91

2.91

2.91

2.91

2.91

2.91

2.91

2.91

2.96

2.96

2.96

2.96

2.96

2.96

2.96

2.96

2.96

2.96

0.00096

0.00097

0.00073

0.00126

0.00129

0.00128

0.00353

0.00449

0.00716

0.01274

0.00140

0.00097

0.00106

0.00120

0.00132

0.00145

0.00340

0.00450

0.00820

0.01230

3031.25

3000.0

3986.30

2309.52

2255.81

2273.44

842.36

648.11

406.43

228.41

2114.28

3051.55

2792.45

2466.67

2242.42

2041.38

870.59

657.78

360.98

240.65

2572.77

3007.78

3389.38

2388.10

2249.12

2157.41

856.48

652.95

383.71

234.53

Results for experiment in which cross-sectional area was varied

## Constants; length of paper is always 5cm

Depth of paper is always 0.015cm

 Length (cm) Voltage (volts) Current (amps) Resistance (ohms)

Conclusion

If I were to extend this investigation I could use a wider variety of lengths and cross sectional areas, as too increase my database of readings for more certain and accurate conclusions.  To extend this particular aspect, I could look into the reason for some currently unexplained patterns in results.  For example, in both my original experiment, and repeat of the length varying practical I noticed that the reading for 4cm was considerably lower than for 5cm.  The jump was by far the steepest from the set of results, and was seen no where else (except with anomalous results).  Research into why this difference is seen here would be an interesting and relevant way to extend the investigation.  I could also go on to investigate how heat affects the resistance or perhaps how the concentration of sodium chloride solution affects it.

### Bibliography

During this investigation I used several books and web sites all listed below.

Collins GCSE sciences – Physics

CGP revision guides – double science physics

www.bitesize.co.uk

www.s-cool.co.uk

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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