$W$. $K$. Roentgen discovered

If the cathode-anode potential difference in an $X$-ray tube is $10^5 V$,then the maximum energy of an $X$-ray photon can be:

The binding energy of the innermost electron in tungsten is $40 \, keV$. The energy of the characteristic $X$-rays emitted is:

The wavelength of the ${K_\alpha }$ line in copper is $1.54 \mathring A$. The ionisation energy of the $K$ electron in copper in Joules is:

The pressure inside an $X$-ray tube is approximately:

The ratio of the energy of the photon emitted by the $K_{\alpha}$ line to that of the $K_{\beta}$ line is