# Figuring out the frequency of light using a solar cell

1. Mar 1, 2009

### hover

Hey people,

I wanted to try this experiment. My experiment is to shine a light on a solar cell and try to figure out the frequency of the light. I do have some idea on how to do this using energy concepts.

$$E_i+W_n_c=E_f$$

$$E_i$$= initial energy in the system (joules)

$$W_n_c$$= work that isn't conservative (joules)

$$E_f$$= final energy in the system (joules)

I know that when electricity is passing through a wire it has a voltage and a current. Multiply those two together and you get power. However I can't measure amps directly because doing so will fry the circuit and in particular the solar cell. Current is equal to voltage over the resistance of the circuit so I can substitute that in for amps and still find the power. Multiply by the amount of time to pass and you get watts. I'll show it mathematically below.

$$VI=P$$

$$\frac{V}{R}=I$$

$$\frac{V^2}{R}=P$$

$$\frac{V^2t}{R}=W$$

I know this will be the final energy so it goes on the right side of the equation.

$$E_i+W_n_c=\frac{V^2t}{R}$$

Now the initial energy comes from the light source itself which is represented by

$$h\nu=W$$

so I plug it in.

$$h\nu+W_n_c=\frac{V^2t}{R}$$

However I don't think this equation is complete. I feel that I might be missing something. Can someone help me out?

Thanks!!

2. Mar 1, 2009

### f95toli

The only way this experiment could work would be if you were able to use perfectly monochromatic sources with exactly the same intensity.
The problem here is that whereas it is true the energy of a single photon is hf that doesn't tell you anything about how MANY photons are hitting the cell per second; i.e. there is no way to determine the frequency by just measuring the power generated by the cell.