The wavelength of $X-$rays is of the order of

The minimum wavelength of $X$-rays produced in a Coolidge tube operated at a potential difference of $40 \ kV$ is ....... $\mathring{A}$.

The minimum wavelength of $X$-rays produced by an electron accelerated through a potential difference of $V$ volts is proportional to:

Find the $(a)$ maximum frequency,and $(b)$ minimum wavelength of $X$-rays produced by $30 \; kV$ electrons.

The $X$-rays produced by a Coolidge tube consist of . . . . .

Fraunhofer lines of the solar system are an example of