Q. When two monochromatic light of frequency, υ and υ/2 are incident on a photoelectric metal, their stopping potential becomes $V_s/2$ and $V_s$ respectively. The threshold frequency for this metal is :
A) $\frac{3}{2}\upsilon$
B) $2\upsilon$
C) $3\upsilon$
D) $\frac{2}{3}\upsilon$
Explanation
[Solution] $h\upsilon = h\upsilon_0 + eV_s/2$ and $h\upsilon/2 = h\upsilon_0 + eV_s$. Subtracting gives $h\upsilon/2 = -eV_s/2$, which is not physically possible, so no option is valid as the question is printed. No option is correct (bonus question as per source key).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.