Question: The quantum nature of light explains the observations on photoelectric effect as -
Step 1 (Governing Law & Theoretical Basis): [0.5 Mark]
According to Einstein’s Photoelectric Equation, the energy of an incident photon ($E = h\nu$) is utilized in two stages: overcoming the work function ($\Phi_0$) of the metal and providing maximum kinetic energy ($K_{max}$) to the emitted photoelectron:
$$h\nu = \Phi_0 + K_{max}$$Where $h$ is Planck's constant and $\nu$ is the frequency of incident radiation.
Step 2 (Step-by-Step Logical Deduction): [0.25 Mark]
- Rearranging the equation: $K_{max} = h\nu - \Phi_0$.
- Since $\Phi_0 = h\nu_0$ (where $\nu_0$ is the threshold frequency), we get $K_{max} = h(\nu - \nu_0)$.
- This equation demonstrates that $K_{max}$ is a linear function of the incident frequency $\nu$. If $\nu < \nu_0$, $K_{max}$ becomes negative, which is physically impossible, explaining the existence of a threshold frequency.
Step 3 (Final Concluded Answer): [0.25 Mark]
The correct option is (B) the maximum kinetic energy of photoelectrons depends only on the frequency of incident radiation.
💡 EL10 Concept Insight: Think of a photon like a single "bouncing ball" hitting an electron; if the ball has enough energy (high frequency), it kicks the electron out instantly, and the extra energy it had becomes the electron's speed—the brighter the light (intensity), the more balls you throw, but each individual ball's energy depends only on its own speed (frequency).