What determines the hardness of the $X-$rays obtained from the Coolidge tube?

Characteristic $X$-rays are not obtained in the spectrum of a hydrogen atom because,

In $X$-ray spectrum,the wavelength $\lambda$ of the $K_{\alpha}$ line depends on the atomic number $Z$ as:

When the atomic number of the first target is $Z_1 = 64$ and the atomic number of the second target is $Z_2 = 80$,the approximate ratio of the wavelengths of the $K_{\alpha,1}$ and $K_{\alpha,2}$ radiations is .......

The patient is asked to drink $BaSO_4$ for examining the stomach by $X$-rays because $X$-rays are

$\Delta \lambda$ is the difference between the wavelength of the $K_\alpha$ line and the minimum wavelength of the continuous $X$-ray spectrum when the $X$-ray tube is operated at a voltage $V$. If the operating voltage is changed to $V / 3$,then the above difference is $\Delta \lambda^{\prime}$. Then: