In a Coolidge tube experiment, the minimum wavelength of the continuous $X-$ray spectrum is equal to $66.3\, pm$. Then:

The wavelength of $X$-rays decreases,when

The energy of a photon of characteristic $X-$ rays from a Coolidge tube comes from

An $X$-ray tube operates at $50 \, kV$ and $20 \, mA$. The target material has a mass of $1.0 \, kg$ and a specific heat capacity of $495 \, J \cdot kg^{-1} \cdot ^\circ C^{-1}$. One percent of the applied electrical power is converted into $X$-rays,and the remaining energy is used to heat the target. Then:
$(1)$ $A$ suitable target material should have a high melting point.
$(2)$ $A$ suitable target material should have low thermal conductivity.
$(3)$ The rate of rise of temperature of the target is $2 \, ^\circ C/s$.
$(4)$ The minimum wavelength of the emitted $X$-rays is $0.25 \, \mathring{A}$.

Which of the following is accompanied by the characteristic $X-$ray emission?

Moseley measured the frequency $(f)$ of the characteristic $X$-rays from many metals of different atomic number $(Z)$ and represented his results by a relation known as Moseley's law. This law is ($a, b$ are constants)