Question

Monochromatic light is incident on a metal surface of work function $2.2eV$. Photo electrons are emitted from it with a maximum kinetic energy of $0.8eV$. Then the wavelength of incident radiation is:

• A. $6133A^0$
• B. $5133A^0$
• C. $4133A^0$
• D. $7133A^0$

Answer 1

Answer: (C)

$4133A^0$

$KE=\frac{hc}{\lambda }-\phi$
$0.8ev=\frac{hc}{\lambda }-2.2eV$
$\frac{hc}{\lambda }=3\times 1.6\times {10}^{-19}$
$\frac{20\times {10}^{-26}}{\lambda }=3\times 1.6\times {10}^{-19}$
$\lambda =4133A^o$

So, the answer is option (C).