physics
posted by Velaria .
What is the minimum work function for a metal for visible light (wavelengths between 400 and 700 ) to eject photoelectrons?

Does work function=hc divided by initial wavelength.
What would the initial wavelength be? 4x10E7 nm? 
The 400 nm photons would be the ones most capable of ejecting electrons. The work function you calculate with your formula will lead to the maximum work function that would allow ejection, not the minimum.
Work function is expressed in volts. You will have to divide the photon energy by the electron charge, e.