Photoelectric effect is obtained on metal surface for a light having
frequencies \(\mathrm{f}_{1} \& \mathrm{f}_{2}\) where
\(\mathrm{f}_{1}>\mathrm{f}_{2}\). If ratio of maximum kinetic energy of emitted
photo electrons is \(1: \mathrm{K}\), so threshold frequency for metal surface
is \(\ldots \ldots \ldots \ldots\)
(A) $\left\\{\left(\mathrm{f}_{1}-\mathrm{f}_{2}\right)
/(\mathrm{K}-1)\right\\}$
(B) $\left\\{\left(\mathrm{Kf}_{1}-\mathrm{f}_{2}\right)
/(\mathrm{K}-1)\right\\}$
(C) $\left\\{\left(\mathrm{K} \mathrm{f}_{2}-\mathrm{f}_{1}\right)
/(\mathrm{K}-1)\right\\}$
(D) \(\left\\{\left(\mathrm{f}_{2}-\mathrm{f}_{1}\right) / \mathrm{K}\right\\}\)