# Physics Coursework - Factors that affect the resistance of brine-soaked paper

Physics Coursework – Factors that affect the resistance of brine-soaked paper

AIM

I am trying to find out how different factors affect the resistance of brine-soaked paper. I will choose one factor and then do a series of experiments to try to find out how this factor affects the resistance. I have chosen to change the length of the paper.

PREDICTION

I think that when I increase the length of the paper, the resistance will also increase. When I increase the length, I predict that the resistance will also increase by the same amount making the relationship directly proportional.

This is what I think the graph of final results will look like:

I think this will happen because the resistance will drop when the length of the paper is reduced. This is because the ions have a shorter distance to travel through the liquid on the paper when it is a short piece of brine-soaked paper and therefore have less time and less in the paper to collide with the anything. Therefore when the paper is a long piece, the more ions there is, the more collisions that will be made and so the higher the resistance. The ions will need to work harder and will collide with more particles so the resistance will keep increasing every time the paper length is increased and therefore this will happen when double the paper length, the resistance will also double from before.

PLAN

In this investigation, I will soak a piece of chromatography paper in brine water and clip it to a bulldog clip which will be attached to a wire with a crocodile clip and a power supply. I will use an ammeter to measure the current in the circuit and a voltmeter to measure the voltage then divide the voltage by the current to find the resistance. I will change only the length of the paper in each experiment. I will start my experiments with 5cm long paper and up to 10cm. To keep this test fair, I will keep the concentration of the brine water the same each time (0.3mol) and the width of the paper, and the voltage as close to 5v as possible.