When a beam of accelerated electrons hits a target , a continuous `X` - ray spectrum is emitted from the target. Which of the following wavelength is absent in `X` - ray spectrum , if the `X` - ray tube is operating at `40,000 "volts"`?

Options

A. 1.5 Å
B. 1.0 Å
C. 0.5 Å
D. 0.25 Å

Answer

D

Explanation

The minimum wavelength of X rays in the continuous X rays spectrum is
`lamda_("min") = (hC)/(eV) = (12375)/(V) Å`
`therefore lamda_("min") = (12400)/(40000 = 0.31 Å`
hence wavelength less than 0.31 Å is not possible .
`therefore lamda = 0.25 Å` is absent.
Other wavelength can be obtained .