Two identical photocathodes receive light of frequencies $f_1$ and $f_2$. If the velocities of the p

Question

Two identical photocathodes receive light of frequencies $f_1$ and $f_2$. If the velocities of the photoelectrons (of mass $m$ ) coming out are respectively $v_1$ and $v_2$, then

Professor PC Thomas Classes · Answer

(a) : For photoelectric effect, \ according to Einstein's equation,
Kinetic energy of emitted electron \ $=h f-($ work function $\phi)$
$
\begin{aligned}
& 	herefore \quad \frac{1}{2} m v_1^2=h f_1-\phi 	ext { and } \frac{1}{2} m v_2^2=h f_2-\phi \
& 	herefore \quad \frac{1}{2} m\left(v_1^2-v_2^2ight)=h\left(f_1-f_2ight) \
& 	herefore \quad v_1^2-v_2^2=\frac{2 h}{m}\left(f_1-f_2ight)
\end{aligned}
$