Question

The threshold frequency for a metal is 10Hz. When light of wavelength $4000\mathring{A}$ is made incident on it, then:

• A. Photoelectrons will be emitted from it with zero speed.
• B. Photoelectric emission will not be started.
• C. Photoelectrons will be emitted with speed ${10}^{5}m/s^{-1}$.
• D. Photoelectrons will be emitted with speed ${10}^{3}m/s^{-1}$.

Answer 1

The correct option is A Photoelectrons will be emitted from it with zero speed.

Threshold frequency is the minimum frequency at which photoelectrons are emitted out of metal surface.
The frequency of light is given by

$\nu =\frac{c}{\lambda }$

$\nu =\frac{3\times {10}^8}{4000\times {10}^{-10}}$

$\nu =0.00075\times {10}^{18}$
$\nu =0.75\times {10}^{15}Hz$
Given that threshold frequency ${\nu }_0=10Hz$.
Hence, $\nu >{\nu }_o$