Question

The work function of a metal is W and $\lambda$ is the wavelength of the incident radiation. There is no emission of photo electrons when :

• A. $\lambda >hc/W$
• B. $\lambda =hc/W$
• C. $\lambda <hc/W$
• D. $\lambda \le hc/W$

Answer 1

The correct option is A $\lambda >hc/W$

The Einstein's equation for photoelectric effect is: $K{E}_{max}=\frac{hc}{\lambda }-W$

where, $K{E}_{max}=$ maximum kinetic energy of photoelectrons , $h=$ Planck's constant, $c=$ velocity of light, $\lambda =$ wavelength of incident light and $W=$ work function of metal surface.

For emission of photoelectrons, $K{E}_{max}>0$

So, $\frac{hc}{\lambda }-W>0$

or, $\frac{hc}{\lambda }>W$

or, $\frac{1}{\lambda }>W/hc$

or, $\lambda <hc/W$

Thus, for no emission of photoelectrons, $\lambda >hc/W$