Question

The minimum energy necessary to overcome the attractive force between the electron and the surface of silver metal is $7.52\times {10}^{-19}J$. What will be the maximum kinetic energy of the electrons ejected from silver which is being irradiated with ultraviolet light having a wavelength $360\AA$?

• A. $40\times {10}^{-19}J$
• B. $47.68\times {10}^{-19}J$
• C. $55\times {10}^{-19}J$
• D. $154\times {10}^{-18}J$

Answer 1

The correct option is B

$47.68\times {10}^{-19}J$

From Planck's Theory,

$E=hv=\frac{hc}{\lambda }$

Therefore,

Energy absorbed = $\frac{hc}{\lambda }$

= $\frac{6.625\times {10}^{-34}\times 3.0\times {10}^{10}}{360\times {10}^{-8}}$

= $5.52\times {10}^{-18}joule$

Now this energy is used in overcoming forces of attraction between surface of metal and imparting velocity to electron, therefore,

$E_{absorbed}=E$ used in attractive forces + Kinetic energy of electron

$\therefore$ Kinetic energy = $5.52\times {10}^{-18}-7.52\times {10}^{-19}joule$

= $47.68\times {10}^{-19}joule$