connected to a retort stand so that I can vary the distance the light is from the solar cell.

The voltage can be found out by using the formula, voltage = current x resistance, both of which I will know. I will then work out the power output of the solar cell by using the formula, power = voltage x current. In fact, I don’t actually need to work out the voltage, because if power = voltage x current and voltage = current x resistance I can use a new formula of power = resistance x current2.

P=IV V=IR P=I2R

I predict that the greater the distance the lamp is from the solar cell, the less light that reaches the solar cell therefore the cell will produce less power. I also predict that the higher the voltage, the brighter the light and therefore the higher the power. I predicted this by first of all finding some preliminary results to also find some suitable ranges.

I am going to vary the voltage from 0 to 12 volts, as that is the maximum the power supply will go up to. The height of the lamp will vary from 10cm to 50cm away from the solar cell. I have tested these ranges by finding some preliminary results and I found that using a resistance of 10Ω is suitable for fair results.

Firstly, I will connect my circuit using the apparatus above. I will then test the voltage by changing it on the power supply connected to the light. I will find three sets of results and then average them by changing the voltage by one volt every time. Then I will test for light intensity by moving the lamp (attached to a stand) up and down by one centimetre each time in order for the light to move further away from the solar cell.

Observing

My table of results showing for the results I found when I changed the light intensity by moving the lamp up and down on a stand (this is the height on my table).

My table of results showing for the results I found when I changed the voltage of the light by one volt at a time (this is the voltage on my table).

I made all my results as accurate as possible by making my experiment a fair test. I found three sets of results and then found the mean of them to try and get the most accurate results as possible. When I was changing the height of the lamp, I used a ruler and accurately marked each centimetre on the stand to which the lamp was connected. I then moved the lamp down by a centimetre each time in order to get accurate results. When I changed the voltage I used the same power supply and moved the voltage up by one volt each time.

## Analysing

As the height of the lamp increases (meaning that the lamp is further away from the solar cell), the power of the cell decreases. My graph shows this because the line of best fit goes down as the height decreases. This is because as the lamp moves further away from the solar cell, there is not as much light reaching the cell. This means that as solar cells convert light directly into electricity, the amount of photons being converted into electrons will be less. Therefore the power output of the cell will decrease as the lamp moves further away from the cell.

As the voltage of the lamp increases (meaning that the lamp is brighter), the power of the cell increases. My graph shows this because the line of best fit goes up as the voltage increases. This is because as the voltage of the light increases, the light becomes brighter. This means that (opposite to above) more photons are being converted to electrons so that the power will increase as the voltage increase.

My evidence supports my prediction. I predicted that as the voltage increased, the power of the light would increase and I also predicted that as the lamp moves further away from the cell, the power would decrease. My results show that my predictions have been correct. They also tell me that my preliminary results have been accurate as well and that I have carried out fair testing for both tests.

## Evaluating

I got the results by reading the current of an ammeter. I then squared the current and multiplied this by my fixed resistance of 10Ω. This was the power of the solar because I used the formula,

power = resistance x current2.

I did each experiment three times and then found the average. The average power is the result that is plotted on the graphs.

My results are as expected. I am pleased I got the expected results because it therefore means that I used a correct methodology. I also proved my predictions. My data and calculations were also accurate. I only had one anomaly, and this was for the light intensity experiment, with a height of 21cm (this is the one highlighted on the graph). I got my results accurately by using a digital ammeter, which gave the current to two decimal places. If I were to use a more accurate system I would probably note the resistance of the circuit for each reading to check that it stayed at ten. I managed to keep the conditions constant and so these would not need to be changed although a more successful blackout may be useful, or doing the experiment in a dark room (with no artificial or natural light).

I had hoped to get more results for the voltage experiment and get a bigger range for the light intensity experiment but the equipment available meant this was not possible. I would have liked to try the experiment by firstly finding the resistance that gave the solar cell a maximum power. In this way I could have found the highest power that the solar cell would give, instead of it just depending on the light source. I would also have liked to try the experiments with different colours and watts of lights to get some more varied data, which would fit in better with real life situations.

When solar cells/panels are used to provide electricity in homes, they are placed on the roofs of houses. My evidence proves the theory that the nearer the light source is to the cell, the more effective the solar cell is. Also, as the light source (normally the sun) gets darker, the cells are less effective and my results prove this theory by using different voltages. This is why many houses with solar cells should be and are placed on the roofs of south facing houses, in order to ensure the cell receives maximum sunlight.

If possible I would have liked to find at least 5 sets of data in the future to back-up my investigation but I am pleased with my results and they match up with my predictions.