Photoelectric Effect

The work function

W

is given by the equation:

W%20%3D%20%5Cfrac%7Bhc%7D%7B%5Clambda%7D

where:
-

W%20%3D%204%20%5C%2C%20%5Ctext%7BeV%7D

is the work function,
-

h%20%3D%206.626%20%5Ctimes%2010%5E%7B-34%7D%20%5C%2C%20%5Ctext%7BJ%C2%B7s%7D

is Planck's constant,
-

c%20%3D%203%20%5Ctimes%2010%5E8%20%5C%2C%20%5Ctext%7Bm%2Fs%7D

is the speed of light,
-

%5Clambda

is the wavelength of light in meters.
Rearranging the formula to solve for

%5Clambda

, we get:

%5Clambda%20%3D%20%5Cfrac%7Bhc%7D%7BW%7D

Substitute the values:

%5Clambda%20%3D%20%5Cfrac%7B6.626%20%5Ctimes%2010%5E%7B-34%7D%20%5Ctimes%203%20%5Ctimes%2010%5E8%7D%7B4%20%5Ctimes%201.602%20%5Ctimes%2010%5E%7B-19%7D%7D%20%5Capprox%20400%20%5C%2C%20%5Ctext%7Bnm%7D

Thus, the longest wavelength of light that can cause photoelectron emission is 400 nm.

Chapter Questions
1 MCQs