Question

Light of wavelength $\lambda$ strikes a photo emissive surface and electrons are ejected with kinetic energy $E$. If the kinetic energy is to be increased to $2E$, then the wavelength must be changed to${\lambda }^{\prime }$, where.

• A. ${\lambda }^{\prime }=\frac{\lambda }{2}$
• B. ${\lambda }^{\prime }=2\lambda$
• C. $\frac{\lambda }{2}<{\lambda }^{\prime }<\lambda$
• D. ${\lambda }^{\prime }>\lambda$

Answer 1

The correct option is A ${\lambda }^{\prime }=\frac{\lambda }{2}$

$E=h\frac{c}{\lambda }$
Kinetic energy is increased to 2E, new wavelength ${\lambda }^{\prime }$
$\frac{2E}{E}=\frac{\lambda }{{\lambda }^{\prime }}$
${\lambda }^{\prime }=\frac{\lambda }{2}$