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## Homework Statement

You need to design a photodetector that can respond to the entire range of visible light (400 nm - 700 nm). What is the maximum possible work function?

## Homework Equations

E = hf = hc/lambda

## The Attempt at a Solution

For 400nm, I got E = 3.11 eV

and for 700nm I got 1.78 eV.

The solution is that the maximum work function is 1.78eV or less, and I do not understand why because 3.11eV is beyond the threshold for 400nm light to emit right? So shouldn't the answer be 3.11eV or greater?