question_answer 31)

Electrons are emitted with zero velocity from a metal surface when it is exposed to the radiation of wavelength 6800\[\overset{{}^\circ }{\mathop{\text{A}}}\,\]. Calculate threshold frequency (\[{{V}_{0}}\]) and work junction (\[{{W}_{0}}\]) of the metal.

Answer:

When velocity of electron is zero, its kinetic energy will also be zero. .   Absorbed energy = Threshold energy + Kinetic energy     or   of \[\frac{hc}{\lambda }\] = \[{{E}_{0}}\] + 0   \[\frac{6.626\times {{10}^{-34}}\times 3\times {{10}^{8}}}{6800\times {{10}^{-10}}}{{E}_{0}}\] \[{{E}_{0}}=2.923\times {{10}^{-19}}J\] Threshold frequency, \[{{v}_{0}}=\frac{{{E}_{0}}}{h}=\frac{2.923\times {{10}^{-19}}}{6.626\times {{10}^{-34}}}\] \[=4.41\times {{10}^{14}}Hz\]