Question

The threshold wavelength for lithium is $5250A^o$. For photo emission to take place, the wavelength of the incident light must be

• A. More than $5250A^o$
• B. Exactly equal to $5250A^o$
• C. Equal to or more than $5250A^o$
• D. Equal to or less than $5250A^o$

Answer 1

Answer: (D)

Equal to or less than $5250A^o$

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 $(E=\frac{hc}{\lambda })$, the photonic wavelength should be less than equal to threshold wavelength.

Option-D is correct.