Prediction
I would choose to predict that proportionality exists between the sine of the angle and the power output. It would be sensible to think that the larger the angle, the larger the power output. And that at 90 degrees, or when the cell is perpendicular to the light source, the output will be greatest, and hence when the cell is parallel, no output will be given at all (in the ideal situation). However, my task is to prove that it works. By turning the Solar cell away from the direct light source, the surface area affected is decreased. Solar cells rely on photons to work, and if less photons are entering the cell, the less the power output. Thus it would seem sensible to predict that there must be some relationship between the angle and power. The diagram below shows how 2 photons enter the cell ().
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http://www.powerlight.com/solar/se_solar_basics.cfm
Diagram of apparatus
Consideration of the variables
This experiment has many variables that need to be taken into consideration. Firstly the Resistance in the circuit needs to be fixed, as to not effect the readings on the multimeter. The Cell has it’s own internal resistance. And I know this to be between 5 and 10 ohms. Therefore the power output will be greatest at a resistance of 5 ohms. The Resistance box is set at 5 ohms for this reason, and will remain fixed throughout. The light level in the room and from the light source must remain the same throughout, so the cell is prone to the same amount of light. The Temperature in the room should not be affected, and I will allow the cell to be exposed to the lamp for 10 minutes before I begin, to allow the heat from the lamp warm the cell until the temperature settles. The distance between the solar cell and the light source must remain constant. And I will use the ruler and check the distance before every reading is taken. 90
The only variables that should exist are the incident angle of the light to the solar cell, and thus the current and voltage readings, which I will record.
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Method - Experiment
∙ Collect all of the equipment displayed in the diagram of apparatus.
∙ Check that the lamp works, and that the Resistance box is not damaged.
∙ Check the Multimeters are operational, and if needed change battery’s, and change the settings for use with either voltmeter or ammeter (200m).
∙ Set-up the equipment as shown in the diagram of apparatus, and use connecting wires to allow as much space as possible for turning the cell to different angles.
∙ Turn on the lamp, and using the markers on A4 paper under the cell, line it up with the centre of the cell which is perpendicular to the source (90degrees)
∙ Wait 10 minuets with the Multimeters and light source on, to allow the temperature to settle.
∙ Check the light to cell distance, fix at 150mm.
∙ With the cell at 90 degrees, take the readings from the voltmeter and ammeter, and multiply the current and voltage together to get the power output of the cell at that angle.
∙ Repeat this but rotate the cell clockwise and line the cell up with the next marking on the paper until the ‘blackout’ angle is achieved (0 degrees). A total of 10 readings should be taken.
∙ Repeat all of the above again, to take a secondary set of results. These will be used to take an average of readings and help precision and accuracy.
Table of results – example
My table will take this form:
Risk Assessment
All things considered, there are little risks presented with this experiment. I feel confident no special precautions need to be taken to ensure the safety of people partaking, or working near the experiment. The are few dangers which in extreme circumstances could cause a problem is the Light bulb. First because of the heat and the risk of burning a hand, which can be avoided by using a metal cover, not touching the bulb, and a cap over the cover to expose little of the lamp. The electricity supply could also be a danger, but I will ensure the wires are out of the way of tripping over, pulling the plug and causing any problems.
The Results
The experiments worked out sufficiently, in both cases. When the average of both experiments were taken, and plotted on Graph paper, 2 of the points, taken at 90 and 80 degrees, did not fit the pattern. I performed this result again, using the same apparatus, which I had numbered in the case that such a result would be obtained. However, the result was the same. I will explain this occurrence in my evaluation. The Graphs of these results are on a separate sheet of graph paper. To be precise, I performed the experiment twice to ensure no readings were false or I had made a mistake. The results were then processed and I took an average of each result. I could not take results more than two decimal places for accuracy, due to the Multimeters display. If however, I had specialised measuring equipment, this could have been more accurate.
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Tables of Results
Experiment 1
Experiment 2
Average of Results
Evaluation and Conclusion
After analysing the graph, it can be seen that a strait line can be drawn through the points following the first 2. This means that there is some proportionality evident between the sine of the angle and the power output of the solar cell, thus proving the hypothesis. However, it can be seen that the first
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2 readings do not fit this pattern at all (other points do to an extent, due to small errors in accuracy). On my graph, it can be seen that the line doesn’t travel exactly through every point. This is due to small accuracy flaws conducted in the experiment, or times where any fixed variables changed slightly. I am happy that these points are near enough to the line to presume that if the experiment were conducted with better apparatus to rotate the cell, and ensure nothing else changes during readings, all the points would lie on the proportionality line. It also shows that although I conducted my experiment as accurately as possible with the given apparatus, errors still occurred somewhere during the experiment. The 2 points at the beginning that do not fit the pattern are more interesting. Something occurred on both occasions that gave this result. I would suggest this was due to the light emerging from the window frames of the room. When rotating, the cell faced the window frames more and more, and although I tried to block out as much light as possible, some must have reflected onto the cell and thus causing the higher readings. Other than this, the only other possible cause is that as the cell neared the ‘blackout’ angle, more light was reflected on the shiny surface of the cell, and not absorbed giving a power output.
If I were to repeat the experiment, I would choose research a better way of rotating the cell to get a perfect angle each time, as I found it difficult to judge to a degree with my own eyes. Perhaps also find a room with no other possible light sources, to ensure the cell is not affected. I am confident in saying there are little ways in which I could improve this experiment using the apparatus available.