Question

Light of frequency $v$ is incident on a substance of threshold frequency $v_0(v_0<v)$. The energy of the emitted photoelectron will be :

• A. $h(v-v_0)$
• B. $h/v$
• C. $he(v-v_0)$
• D. $h/v_0$

Answer 1

The correct option is A $h(v-v_0)$

Einstein explained the phenomenon of photo electric effect on the basis of Planck's theory. According to which the kinetic energy of photo-electrons emitted from the metal surface is $E$ and $\varphi$ is the work function of the metal, then

$E=hv-\varphi$ ...(i)

where $hv$ is the energy of the photon absorbed by the electron in the metal. If for a given metal, the threshold frequency of light be $v_0$ then an amount of energy $h{v}_0$ of the photon of light will be spent in ejecting the electron out of the metal.

ie, $\varphi =h{v}_0$ ...(ii)

From equations (i) and (ii), we get

$E=hv-h{v}_0$

$\Rightarrow E=h(v-v_0)$