Which of the following wavelengths in $\mathring{A}$ represents 'hard' $X$-rays?

If $10000\, V$ is applied across an $X$-ray tube,what will be the ratio of the de-Broglie wavelength of the incident electrons to the shortest wavelength of $X$-rays produced? (Given: $\frac{e}{m}$ for an electron is $1.8 \times 10^{11}\, C\, kg^{-1}$)

An $X$-ray tube operates at $30 \ kV$. What is the minimum wavelength emitted in $\mathring{A}$? (Given: $h = 6.6 \times 10^{-34} \ J \cdot s$,$e = 1.6 \times 10^{-19} \ C$,$c = 3 \times 10^8 \ m/s$)

Calculate the wavelength of the $K_{\alpha}$ line for $Z=31$, when $a=5 \times 10^7 \, Hz^{1/2}$ for a characteristic $X$-ray spectrum.

The characteristic $X$-rays depend on .........

Consider a photon of continuous $X$-ray and a photon of characteristic $X$-ray of the same wavelength. Which of the following is different for the two photons?