Question

The frequencies of X-rays, $\gamma$ rays and Ultra violet rays are respectively incident on a metal, having work function is $0.5eV$. The ratio of maximum speed of emtted electrons is

• A. $p<q,q>r$
• B. $p>q,q>r$
• C. $p<q,q<r$
• D. $p>q,q<r$

Answer 1

The correct option is A $p<q,q>r$

Maximum speed of emitted electrons $\frac{1}{2}m{v}^2=h{\nu }_{incident}-{\varphi }_{metal}$
where ${\varphi }_{metal}=0.5eV$ is the work function of the metal and ${\nu }_{incident}$ is the frequency of incident radiation.
Increasing order of frequency : Ultra violet rays < X-rays < $\gamma$ rays
Thus increasing order of maximum speed of emitted electrons : Ultra violet rays < X-rays < $\gamma$ rays
$⟹r<p<q$
So option A is correct.