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 $$\mu$$A. 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! :)