Q. The work function ($\Phi$) of some metals is listed below. The number of metals which will show photoelectric effect when light of 300 nm wavelength falls on the metals is : [table] Metal | Li | Na | K | Mg | Cu | Ag | Fe | Pt | W ; $\Phi(eV)$ | 2.4 | 2.3 | 2.2 | 3.7 | 4.8 | 4.3 | 4.7 | 6.3 | 4.75 [/table]
A) 2
B) 4
C) 6
D) 8
Explanation
(b)
Energy of photon$= \frac{hc}{\lambda}J = \frac{hc}{e\lambda}eV$
$= \frac{6.625 \times 10^{- 34} \times 3 \times 10^{8}}{300 \times 10^{- 9} \times 1.602 \times 10^{- 19}} = 4.14\ eV$
For photoelectric effect to occur, energy of incident photons, must be greater than work functions of metal. Hence, only Li, Na, K and Mg have work functions less than 4.14 V.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.