Question

The maximum velocity of an electron emitted by light of wavelength $\lambda$ incident on the surface of a metal of workfunction $\varphi$ is where h $=$ Planck’s constant, m $=$ mass of electron and c=speed of light

• A. $[\frac{2(hc+\lambda \varphi )}{m\lambda }{]}^{\frac{1}{2}}$
• B. $\frac{2(hc-\lambda \varphi )}{m}$
• C. $[\frac{2(hc-\lambda \varphi )}{m\lambda }{]}^{\frac{1}{2}}$
• D. $[\frac{2(hc\lambda -\varphi )}{m}{]}^{\frac{1}{2}}$

Answer 1

The correct option is C $[\frac{2(hc-\lambda \varphi )}{m\lambda }{]}^{\frac{1}{2}}$

Maximum K.E. $=$ incident energy - work function

$\frac{1}{2}m{v}^2=\frac{hc}{\lambda }-\varphi$

$v=[\frac{2(hc-\lambda \varphi )}{m\lambda }{]}^{1/2}$
So, the answer is (C).