The minimum frequency of light needed to eject electrons from a metal is called the threshold frequency, ν0.

a) Find the minimum energy needed to eject electrons from a metal with a threshold frequency of 2.78 × 10ˆ14 s–1.

b) With what kinetic energy will electrons be ejected when this metal is exposed to light with a wavelength of λ = 245 nm?

Part a) Planck relationship: E = h×ν ν = frequency in s^-1 Hz
where h is the Planck constant = 6.626×10^-34 J s
E = (6.626×10^-34)×2.78×10^14 = 1.84×10^-19 J per photon
Part b) E = h×c/λ
Planck constant h = 6.626×10^-34 J s c = speed of light = 3.00×10^8 m s-1
λ wavelength in m = 245×10^-9 m
E (6.626×10^-34)×(3.00×10^8)/(245×10^-9) = 8.11×10^-19 J per photon
hν = W + E(k) (Einstein)
W = the minimum energy required to remove an electron from the surface of the metal;
E(k) = kinetic energy of the ejected electron
Ek = 8.11×10^-19 - 1.84×10^-19 = 6.27×10^-19 J per photon
[1] http://www.science.uwaterloo.ca/~cchieh/…