Chapter 28, Problem 26Q

To determine

Why cut-off wavelength implies photon nature for light.

Answer to Problem 26Q

Solution:

Since at cut-off wavelength, transition of electron from high energy state to low energy state take place.

Explanation of Solution

At cut-off wavelength, the electron moves from outer orbit to inner orbit by emitting some energy in form of photon. Hence the cut-off wavelength represents the photon nature of light.