$X$-rays region lies between

$X$-rays were discovered by

The wavelength of the ${K_\alpha}$ line for an element of atomic number $29$ is $\lambda$. Then the wavelength of the ${K_\alpha}$ line for an element of atomic number $15$ is (Take Moseley's constant $b = 1$ for both elements).

The variation of wavelength $\lambda$ of the $K_{\alpha}$ line with atomic number $Z$ of the target is shown by the following curve of

$(a)$ An $X$-ray tube produces a continuous spectrum of radiation with its short wavelength end at $0.45\,\mathring{A}$. What is the maximum energy of a photon in the radiation?
$(b)$ From your answer to $(a)$,guess what order of accelerating voltage (for electrons) is required in such a tube?

The wavelength of $X$-rays decreases,when