An experiment to investigate how the resistance between two copper plates immersed in copper sulphate solution varies with the surface area of the plates.
James Goldsack 10.5 Physics coursework Bristol Grammar School
An experiment to investigate how the resistance between two copper plates immersed in copper sulphate solution varies with the surface area of the plates.
Introduction
This experiment investigates how the resistance of a copper sulphate solution changes as the surface area of two copper plates (electrodes) immersed in the solution changes. The two plates will be placed in the solution and depth of the solution varied by adding solution. The voltage between the plates will be measured with a voltmeter and the current will be measured with an ammeter. The resistance will then be calculated using Ohm’s law, dividing the voltage by the current. Readings will be taken every 5mm up the copper plates to give a wide range of results.
Prediction
I predict that when the depth of the copper sulphate solution, and hence the surface area of the copper plate immersed in the solution, is doubled, the resistance will halve. This means that the reciprocal of the surface area is directly proportional to the resistance as shown in graph 1. This is because there is double the amount of material for the electrons to move through so more can flow through the solution at one time. This is also the same as Resistance being directly proportional to the reciprocal of the surface area of the copper plates and hence to the volume of liquid between them.
Equipment
Here is a list of equipment which should be set up as in diagram 1:
- 1 power supply set at 4 volts
- 1 beaker
- 2 copper plates
- 1 ammeter - 1 to 10 amps
- 1 voltmeter - 1 to 20 volts
- 1 connection block
- 1 measuring cylinder
- 1 ruler
- 5 wires
- 1 thermometer
Plan
For this experiment, different depths of 0.5M copper sulphate solution were put into a beaker with two copper plates. The plates were a fixed distance apart and the same ones were used throughout the experiment. Therefore, by increasing the depth, the volume increases and the immersed surface area of the copper plates also increases in proportion. The voltage across the copper sulphate solution and the current were recorded and the resistance was found by dividing the voltage by the current.
- The voltage from the power supply was set at 4 volts because any greater a voltage would have begun to heat up the copper sulphate and the temperature needs to be kept as constant as possible and monitored.
- The only thing that can change is the depth of the copper sulphate solution as that is the independent variable. Everything else has to be kept the same or monitored to make sure that they aren’t having an effect on the results.
- The equipment was set up as in diagram 1 and the first set of readings was taken with no copper sulphate solution in the beaker.
- Copper sulphate solution was then added so that it covered 1cm of the plates’ height. As the plates were 2cm wide and 6cm apart, this gave a volume of 12cm3 of the copper sulphate solution between the plates. The readings were taken and recorded.
- More copper sulphate solution was added so that another centimetre of the plates was covered. The readings were taken and recorded.
- The previous stage was repeated for 3cm, 4cm, 5cm, 6cm, 7cm, and 8cm of the plates covered.
- For all of the readings, a thermometer was put into the beaker to measure the temperature so that any fluctuations could be noted. However, as the copper sulphate solution all came from the same container, it stayed very even throughout.
- Safety goggles were worn to prevent any copper sulphate getting into eyes and lab coats were worn to prevent damage to clothes.
