Question

A sodium surface is illuminated with light of wavelenght 300nm. The work function of the metal is 2.4eV.

1. Determine the K.E
2. The cutt-off wavelenght of sodium​

Answer 1

1) 1.67eV

2) 505nm

Step-by-step explanation:

The maximum kinetic energy of photoelectrons ,

KEmax=λhc−W=(0.3×10−6)(1.6×10−19)(6.62×10−34)(3×108)eV−2.46eV=1.67eV

If λ0 is the cut-off wavelength, W=λ0hc

or λ0=Whc=2.46×1.6×10−19(6.62×10−34)(3×108)=5.05×10−7m=505×10−9=505nm

We know that the work function is the minimum photon energy for taking place of photoelectric effect.