• # question_answer When silver is irradiated by ultraviolet light of $1000\overset{\text{o}}{\mathop{\text{A}}}\,,$potential of 7.7 V is required to stop the photo electrons. The work function of silver will be: A)  3.72 eV         B)  6.72 eV C)  5.72 eV        D)  4.67eV

From Einsteins theory, maximum kinetic energy $({{E}_{k}})$of emitted photoelectron is given by ${{E}_{k}}=hv-W$ Where W is work Function of silver,$v$is frequency. $\Rightarrow$ $W=\frac{hc}{\lambda }-{{E}_{k}}$ Putting $h=6.6\times {{10}^{-34}}\,J-s,$ $c=3\times {{10}^{8}}\,m/s,\,\lambda ={{10}^{-7}}\,m$ ${{E}_{k}}=7.7\,eV$ $=7.7\times 1.6\times {{10}^{-19}}V$ $\therefore$ $W=\frac{6.6\times {{10}^{-34}}\times 3\times {{10}^{8}}}{{{10}^{-7}}}$ $-7.7\times 1.6\times {{10}^{-19}}J$ $\Rightarrow$$W=19.8\times {{10}^{-19}}-12.32\times {{10}^{-19}}$ $\Rightarrow$ $W=7.48\times {{10}^{-19}}$ $W=\frac{7.48\times {{10}^{-19}}}{1.6\times {{10}^{-19}}}eV$ $=4.67\,eV$