Question

The work function for a metal is 2.4 eV. What is the minimum photon frequency that can just eject an electron from the metal?

Answer 1

The expression for the photoelectric effect is -  

Kmax = h * f - ?

where:

Kmax is the maximum kinetic energy of the ejected electron
h is planks constant
f is the frequency of the incident photon and
? is the work function, which is the minimum energy required to remove an electron from the surface of any given metal, so:

For the limiting condition,

Kmax = 0

so,

? = h * f0
where f0 is the minimum photon frequency,

therefore,

f0 =  ? / h

put the values -

f0 = (2.4 x 1.6 x 10^-19) / (6.626 x 10^-34) = 0.5795 x 10^15 Hz = 5.795 x 10^14 Hz

So, the minimum photon frequency = 5.795 x 10^14 Hz.