Question

In a photoelectric experiment, the stopping potential for incident light of wavelength 4000 Å is 2 V. If the wavelength is changed to 3000 Å, the new stopping potential will be approximately:

• A. 2 V
• B. 3.03 V
• C. 4.14 V
• D. 1.5 V

Hint:

Shorter wavelength means higher energy photons, which results in higher stopping potential.

Answer 1

The Correct Option is B

Step 1: Concept
Einstein’s photoelectric equation: $eV_s = \frac{hc}{\lambda} - \phi$.

Step 2: Meaning
Energy of photon $E = \frac{12400}{\lambda (\text{\AA})}$ in eV. For 4000 \AA, $E_1 = 3.1$ eV. Since $V_{s1} = 2$ V, work function $\phi = 3.1 - 2 = 1.1$ eV.

Step 3: Analysis
For 3000 \AA, $E_2 = \frac{12400}{3000} \approx 4.13$ eV. New stopping potential $V_{s2} = E_2 - \phi = 4.13 - 1.1 = 3.03$ V.

Step 4: Conclusion
The new stopping potential is approximately 3.03 V.
Final Answer: (B)