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# An X-ray tube operates on $30\: kV$. The minimum wavelength emitted is :

$\begin {array} {1 1} (a)\;6.6\: A^{\circ} & \quad (b)\;1.2\: A^{\circ} \\ (c)\;0.133\: A^{\circ} & \quad (d)\;0.4\: A^{\circ} \end {array}$

Ans : (d) $0.4 \: A^{\circ}$
$\lambda_{min} = hc/eV$
$= 6.6 \times 10^{-34} \times 3 \times 10^8 / (1.6 \times 10^{-19} \times 30 \times 10^3 ) = 0.4 A^{\circ}$

edited Mar 13, 2014