Couple of questions on the behaviour of a Solar CEll

[type_writer]

Hey guys,

Homework Statement

Im doing my physics coursework atm and its on the subject of Solar cells and am changing a few variables and observing how the voltage of the solar cell changes. I am also measuring the current and using that to calculate the Power output. the caluclations are easy, its explaining why my data is the way it is is the issue.

the first thing i did was rotate the solar cell in 10 degree increments relative to the light source. the power output vs rotation looked like the following:

http://img821.imageshack.us/img821/4315/rotation.jpg
(sorry for the drawing, i don't have the graphs at hand).

The other graph was a power against an increasing load resistance. on the graph, the power shot up and then slowly decreased, which, to me suggested i ought to use a logarithmic axis scale (base 10). this graph looked like this:

http://img651.imageshack.us/img651/5102/rload.jpg

Any ideas why it does this and the physics behind it?Thanks for any help, its much appreciated. any issues with the image hosting, just say and ill try to find an alternate host.

EDIT: just incase i didnt make it clear, in all of these graphs, power is on the y-axis and rotation or Rload is on the x.
EDIT2: just saw the dodgy looking title. how do i change it?

 

[jbsteele]

Homework EquationsP=VIThe Attempt at a SolutionIn the first graph, the power output increases until it reaches a peak and then decreases as the solar cell is rotated further away from the light source. This is because the angle of incidence between the light and the solar cell is maximised when the cell is perpendicular to the light source. As the angle of incidence decreases, the intensity of light that the cell is exposed to is reduced and so the power output is lower.In the second graph, the power output increases as the load resistance is increased. This is because, as the resistance increases, more current is drawn from the solar cell. As power is equal to voltage multiplied by current, more current results in more power. However, as the resistance is increased further, the current begins to decrease since some of the energy is lost due to the resistance. This results in a decrease in power output. The logarithmic scale is used because the power output changes exponentially with resistance.