If the wavelength of light in an experiment on photoelectric effect is increased, then
(A) the photoelectric emissions will not take place
(B) the photoelectric emission may or may not take place
(C) the stopping potential will increase.
(D) the stopping potential will decrease
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (B) and (D) only **
Given: Wavelength of light $\lambda$ is increased in a photoelectric experiment.
Photon energy: $E = h\nu = \frac{hc}{\lambda}$
Maximum kinetic energy of emitted electrons: $K_\text{max} = h\nu - \phi$, where $\phi$ is the work function.
Stopping potential: $V_s = \frac{K_\text{max}}{e} = \frac{h\nu - \phi}{e}$
Effect of increasing $\lambda$:
- Frequency decreases: $\nu = c / \lambda$ decreases
- If $\nu > \nu_0$ (threshold frequency), photoelectric emission still occurs, but $K_\text{max}$ decreases → stopping potential decreases
- If $\nu < \nu_0$, emission does not occur
✅ Therefore:
• Photoelectric emission may or may not take place → (B)
• Stopping potential decreases → (D)
Answer: (B) and (D)