How do you find the work function and cutoff Wavelength?

Question

In a photoelectric experiment using a sodium surface you find a stopping
potential of 1.85 eV for a wavelength of 300 nm. Find the work function for
sodium and the cutoff wavelength for sodium.

Answer 1

The maximum kinetic energy K is related to stopping potential V by:

K = Ve

where e is the elementary charge. Max K is also equal to:

K = hf - φ = hc/λ - φ

where φ is the work function of the metal. Substituting the first equation above into the second equation, and solving for φ we get:

φ = hc/λ - Ve

You have λ (300 nm), Ve (1.85 eV), and for simplicity, hc = 1240 eV·nm. Plug those numbers into the equation to find the work function.



The work function φ is also equal to hc/λ, where in this case λ is the threshold (or cutoff) wavelength. λ = hc/φ.

Answer 2

Work Function Equation

Answer 3

how we can know if the cut off wavelength is in maximum or minimum??