Question

Assertion :The threshold frequency of photoelectric effect supports the particle nature of light
Reason: If frequency of incident light is less than the threshold frequency, electrons are not emitted from metal surface

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (B)

There is no emission of photoelectrons till the frequency of incident light is less than a minimum frequency, however intense light it may be. In photoelectric effect, it is a single particle collision. Intensity is $h\upsilon \times N$, where $h\upsilon$ is the individual energy of the photon and $N$ is the total number of photon. In the wave theory, the intensity is proportional, not only to ${\upsilon }^2$ but also to the amplitude squared. For the same frequency, increase in intensity only increase the number of photons (in the quantum theory of Einstein).