Q. Monochromatic radiation emitted when electron on hydrogen atom jumps from first excited to the ground state irradiates a photosensitive material. The stopping potential is measured to be $3.57\ V.$ the threshold frequency of the material is
A) $4 \times 10^{15}Hz$
B) $5 \times 10^{15}Hz$
C) $1.6 \times 10^{15}Hz$
D) $2.5 \times 10^{15}Hz$
Explanation
(c) $n \rightarrow 2 - 1$
$E = 10.2\ eV$
$kE = E - \phi$
$Q = 10.20 - 3.57$
$hv_{0} = 6.63\ eV$
$v_{0} = \frac{6.63 \times 1.6 \times 10^{- 19}}{6.67 \times 10^{- 34}} = 1.6 \times 10^{15}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.