To perform this experiment I will need some apparatus. This will consist of:-
- 30cm ruler
- A Pen
- Card
- Lamp with 60watt bulb
- Milliamp meter
- Solar cell
- Connecting wires x2
- Crocodile clips x2
Solar cell measurements
These are the following measurements of the solar cell i will be using in this experiment:-
- 100% - 91mm x 63mm
- 75% - 68.25mm x 47.25mm
- 50% - 45.5mm x 31.5mm
- 25% - 22.75mm x 15.75mm
Diagram
Below is a labelled diagram of how the experiment is going to be set-up:-
Method
This is the procedure that I will use to do the experiment:-
- Set up apparatus as in shown in the diagram.
- Measure the distance from the lamp to the solar panel.
- Test the card whether it is opaque or not.
- Set milliamp meter to 200 milliamps.
- Record the measurement of the milliamps shown on milliamp meter.
- Then, repeat the experiment two more times to gain a average and precision with the following area of the solar panel covered (%):-
- 25, 50, 75, 100.
- After use of all apparatus, put back in the correct places.
- After that, I calculate the readings for the area of the solar panel uncovered using a PC program called “Microsoft Excel” to illustrate tables and graphs.
Accuracy and Range of Readings
To make this experiment as accurate as possible we needed to make sure that the distance length from the solar panel to the lamp is accurate every time so we checked the distance length was 10.5cm before we started a reading. Also we tried not to keep it too far away because as you get further away, the light from the bulb gets more spread out meaning that less of it hits the solar panel. If it is too close the temperature will affect the readings. Milliamp meter needs to be set at 200 Milliamps range at all times. We needed to also ensure that the time intervals between readings were about 10 seconds. The card had to be folded four times to make it fully opaque so no light can pass through. We took the readings of the current immediately so the card wasn’t under the lamp too long which may be a risk to fire. After each reading we turned the lamp off as it may affect the results if we kept it on for too long, which would make the temperature increase. To make my experiment as reliable as possible I will repeat it 3 times and then find an average result
using the ‘arithmetic mean’.
Arithmetic Mean = ∑ x
n
Where:-
‘∑’ is a capital Greek letter (sigma). ‘∑x’ means the sum of all the terms and ‘n’ is the number of terms. I will use this formula to calculate my ‘Average current’ and for the ‘mean of graph’ (this allows me to work out the exact point where the line of best fit runs straight through).
Safety
Keeping a safe experiment is also very important for the safety of me and other people around me. To ensure that my experiment is safe, I will carry out the following precautions:-
- I must check if there are any breakages in the wire of the lamp.
- I must make not to touch the light bulb when the lamp is on and has been used as it may be very hot.
- I must not keep the solar panel under the lamp for too long to prevent a risk of a fire.
- I must also not keep the card under the lamp for too long as they could be a risk of a fire.
- I will handle all electrical equipment with dry hands to prevent electrical shocks.
- Tuck stools in to prevent no-one falling in the lab.
- Put all bags under the table to prevent no-one falling in the lab.
- Never run in the lab.
- I should act in a sensible and safe manner, carefully working with the equipment in the correct way and being aware of any dangers.
➔ Obtaining Evidence
Results Table:
*I have rounded my results to 1 decimal places to allow them become as accurate as possible
Graph – Line of Best Fit
➔ Analysing and Considering Evidence
During our investigation it was found that when we directed the bulb at the solar panel the light energy was converted to electrical energy. I have analysed my data and presented them in graphical form. The graph above shows the averages between the three experiments. All of the results between the three experiments were very similar showing I had reliable results. From looking at my tables and graphs I can say that my prediction was correct i.e. as area uncovered increased current increased. This is because more photons hit the semi conductor device, resulting in more electrons being released and more electric current. From the graph I can see the current was linear up to 50% than it curved and became nonlinear.
Possible reasons for this:-
- This means that as more area is uncovered, fewer photons are hitting the semi conductor device because a certain 60 watt bulb can only produce a certain amount of photons.
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Another possibility could be because there is more area for the photons to hit; some of them could possibly concentrate on one bit of the area than the other bits as the rays are less concentrated and more spread out over a greater distance. There must also be an increase in resistance. Current flowing through the conductor may encounter resistance. Any resistance they encounter inside the source is called the internal resistance which has removed energy from the charges before they have a chance to leave the source. This basically means wasting the source’s energy. The temperate from the bulb’s light intensity on the area of the cell could have also affected the increase in resistant.
- Another possibility could also be caused by internal resistance inside the solar cell meaning that as more light is put onto the solar panel with the more of it uncovered, more current is being produced, so thus meaning more current will mean more resistance would appear. On the day of the experiment there was light source coming through the window and from the ceiling light which could have also affected how many photons hit the semi conduct device. There were also light sources from other group’s experiments. There would be more of significance if we did the experiment in a room completely dark without any light source than in a lab with quite a few light sources.
- We may have also rushed the experiment and not taken the time to let the voltmeter settle on the correct voltage, as it has a tendency to fluctuate across a range of values before stopping.
My predictions were in some cases correct and the results and graph shows this but also the results shows that some of my predictions were wrong i.e. I predicted the 0% uncovered would be 0, this was correct because no light was to get through and produce a current, my 100% prediction was right but not that accurate, I predicted that the 100% uncovered would be the highest reading and it was and I was almost correct with the predicted reading but I was a few milliamps out. As for my predictions for the 25%, 50% and 75%, these were not correct and not very accurate, this could be for a couple of reasons i.e. the temperature of the light bulb made a change in the readings, as my results were approx 10-15 milliamps out in each prediction. I found all the information that explained the relationship between the resistance and the length; this is why my results agreed with my description of the solar cell.
Overall I believe the experiment worked well because my prediction that was totally correct because as area uncovered increases, current increases. However, the graph wasn’t linear as there wasn’t a straight line all the way up so the increased wasn’t as expected. This is for reasons of have explained earlier in my analysis.
➔ Evaluating
The method made in the preliminary work, which we further used in the experiment worked well we got all the main points needed to do the experiment, but I think that some aspects used in the method could be changed because this may of changed the results given, this was the distance the light was from the solar panel, it was only 10.5cm, maybe it could of done being around 15-20cm in distance.
All of the results between the three experiments were very similar showing I had reliable results.
I believe that my results, in general, were reasonably accurate. I know that because I used a milliammeter which was digitally calculated, instead of an analogue one. My results on the graph lied on a straight line until 50% then after that it had two slight anomalies (circled in red).
I believe that this happened because of the temperature from the bulb. The crocodile clips were not always fixed securely to the wire with a good connection. This also meant that they were easy to move about on the wire, changing the length of it.
When it came to accuracy during this experiment, it was slightly difficult to maintain. For example, we had to keep the semi conduct device in the same place. This was hard to maintain, because we had to change the card each time and this moved the semi conduct device slightly each time. To solve this I would use four semi conduct device with the card taped to it in the right place, then I would mark out in pencil where the semi conduct device was initialling before I changed it. Another was trying to keep it as much away from any other light source in the lab, but this was also hard to maintain as there was couple of windows in the lab with sun shining through and ceiling light. Since there was more than just our group working in the room we really could have done with working alone in another separate room without any other interference from the lights of other groups. To solve this problem I would conduct the experiment in a dark room no background light and the results would be much more accurate.
I could have improved my investigation to support my analysis by doing other experiments such as the following:-
- The distance from the lamp to the solar cell:
I believe that as the distance between the lamp and solar cell is increased, the resistance would decrease. This is because the temperature would not affect the experiment as much.
I think the more uncovered the more resistance there would be due to internal resistance.
- Use a clamp and stand holding a bulb than a lamp for accuracy of the angle the light source is at.
- Changing the light intensity of the bulb.
- The angle at which the light hits the solar panel.
- I would try conducting the experiment in a room without any light source to give more accurate and less anomalous results.
No really problems occurred during the experiment, the only thing annoying me was the milliamp meter took time to settle on the correct milliamp, as it has a tendency to fluctuate across a range of values before stopping.
I think that my results are good enough to support the firm conclusion that as the percentage area uncovered increases; more photons will hit the semi conductor device, meaning more electrons will be released resulting in more electric current because all of the results between the three experiments were very similar showing I had reliable results.
To carry this experiment on further, the tests could be done more times to see if the averages are still the same, to see if there is a change in results if the room is completely dark i.e. so no natural light can interfere with the tests, using a more stronger or sensitive solar panel to pick up the light. I would also increase the area in smaller steps e.g. 10%, 20% because I feel I didn’t take enough results. Five results is only just enough to give me a conclusion so having more would also give me a better conclusion.
Overall, I would say the experiment turned out successful and I was very happy with the investigation and my results.