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

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Carol Bhaskar        11HEA                                        January 2002    

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.

 

Planning

        This experiment involves 2 independent variables – length and cross-sectional area.  The experiment will be carried out using a circuit shown below. It uses these components, 2 cells, a voltmeter (in parallel with the brine soaked paper), a milli-ammeter (in series) and 2 bulldog clips.

 

Method

        

The above circuit will be constructed by connecting two bulldog clips into a series circuit.  In-between these, is where the brine soaked chromatography paper will lie (the bulldog clips will hold this, connecting it to the circuit). The ammeter will also be set in this series circuit.  The voltmeter is in parallel with the bulldog clips and paper.

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Pieces of chromatography will be cut, and then soaked in salt water.  Pieces of chromatography paper ranging from 10cm to 1cm in length (1cm steps, 10 readings in all), will be soaked in brine, the bulldog clips will hold these in place connecting the paper to the circuit.  A reading from the ammeter and voltmeter will be taken, and the next piece of paper prepared.  This will be repeated once for each reading to ensure accuracy.  To ensure that this is a fair test the paper will always be of the same kind, 4cm in width, and 0.15mm in depth, ...

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