The ionisation energies of K-shell for cobalt, copper, and molebdenum are 7.8, 9.0 and `20.1 KeV` respectively. If any metal out of these is used as target in an X-ray tube operated at `15KV`, then
(a) the K-series of characteristic X-rays will be emitted only by cobalt
(b) the K-series of characteristic X-rays will be emitted only by cobalt & Cu
(c) the K-series of characteristic X-rays will be emitted only by cobalt, Cu , Co and Mo
(d) the minimum wavelength of continuous X-rays emitted by the three metals will be same

Options

A. The K–series of characteristic X-ray will be emitted by Co only
B. The K–series of characteristic X–rays will be emitted by Cu and Co only.
C. The K–series of characteristic X–rays will be emitted by Cu, Co and Mo.
D. The minimum wavelength of continuous X–rays emitted by the three metals will not be same.

Answer

B