What is the Minimum Detectable Power of a Light Flash on a Silicon Solar Cell?

[Sarah88]

Homework Statement

A circuit employs a silicon solar cell to detect flashes of light lasting .25 seconds. The smallest current the circuit can detect reliably is .42 \muA. Assuming that all photons reaching the solar cell give their energy to a charge carrier, what is the minimum power of a flash of light of wavelength 550 nm that can be detected?

Homework Equations

E= h*f
f= c/wavelength

The Attempt at a Solution

I first found the energy by h*(c/wavelength) --> 6.63*10^-34 m^2 kg/s * (3*10^8 m/s)/(550*10^-9 m) = 3.62*10^-19 J. Since 1 W= 1 J/s, I took the energy and divided it by the time of .25 seconds (to get an answer of 1.45*10^-18 W). However, this answer is wrong, was I wrong in neglecting the current in the circuit? Does this end up changing the J of energy? I know P can equal I*V, or I^2*R, but I'm not sure how to incorporate power with current in this sort of problem. Thank you!

 

[gneill]

Think in terms of counting how many photons are required. The problem states (essentially) that each photon can produce a charge carrier for the current. How many charge carriers does it take to produce the required current for the required time?

 

[Sarah88]

Ok, that makes sense, thank you! :)