Question

Threshold wavelength for lithium metal is $6250\mathring{A}$. For photo emission, the wavelength of the incident light must be ___________.

• A. Exactly equal to $6250\mathring{A}$
• B. More than $6250\mathring{A}$
• C. Equal to or more than $6250\mathring{A}$
• D. Equal to or less than $6250\mathring{A}$

Answer 1

The correct option is D Equal to or less than $6250\mathring{A}$

The threshold wavelength of a material signifies that if the photons of energy corresponding to this wavelength or higher strike onto the material, they will undergo photo electric effect. As the energy of a photon is inversely proportional to wavelength (E=λhc​), the photonic wavelength should be less than equal to threshold wavelength.

Option-D is correct