Question

Five volt of stopping potential is needed for the photoelectrons emitted out of a surface of work function 2.2 eV by the radiation of wavelength

• A. $1725\stackrel{o}{A}$
• B. $3444\stackrel{o}{A}$
• C. $861\stackrel{o}{A}$
• D. $3000\stackrel{o}{A}$

Answer 1

The correct option is A $1725\stackrel{o}{A}$

The Einstein's equation for photoelectric effect is $eV=\frac{hc}{\lambda }-W$

or $\lambda =\frac{hc}{[eV+W]}=\frac{(6.626\times {10}^{-34})\times (3\times {10}^8)}{(1.6\times {10}^{-19}\times 5)+(2.2\times 1.6\times {10}^{-19})}=1.725\times {10}^{-7}m=1725\times {10}^{-10}m=1725A^0$