Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.
Assertion A: Number of photons increases with increase in frequency of light.
Reason R: Maximum kinetic energy of emitted electrons increases with the frequency of incident radiation.
In the light of the above statements, choose the most appropriate answer from the options given below:

Solution

Physics sir · 4 steps

Frequency sets the energy of each photon, not how many photons arrive. Keep those two ideas apart.

1. Check Assertion A. For light of power P, the number of photons arriving per second is n = P/hν. At the same intensity, raising ν makes each photon carry more energy, so fewer photons arrive. The photon number depends on intensity, not on frequency, so A is not correct.
2. Check Reason R. Einstein's photoelectric equation links the fastest electron's energy to the frequency of the incident light.

   Kₘₐₓ = hν - φ₀

3. Read the equation. The work function φ₀ is fixed for a given metal, so Kₘₐₓ rises linearly with ν. R is correct.
4. So. A is wrong and R is right, which is option (a).

The idea to keep. Intensity decides how many photons and so how many photoelectrons. Frequency decides the energy of each photon and so Kₘₐₓ. Never swap these two roles.

Answer from the NTA final answer key. Solution by PrepWiser.