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# The maximum frequency of X-rays produced by 30 kv electrons is

$\begin {array} {1 1} (a)\;7.24 \times 10^{20}\: Hz & \quad (b)\;72.4 \times 10^{20}\: Hz \\ (c)\;7.24 \times 10^{18}\: Hz & \quad (d)\;72.4 \times 10^{18}\: Hz \end {array}$

Potential of the electrons, $V = 30\: kv=3 \times 10^4V$
Hence, energy of the electrons, $E=3 \times 10^4eV$
Maximum frequency produced by the X-rays = $v$
The energy of the electrons is given by the relation :
$e=hv\: \: \: \:$ where, $h$= planck's constant $= 6.626 \times 10^{-34} Js$
so, $v = E/h$
$= ( 1.6 \times 10^{-19} \times 3 \times 10^4) / 6.626 \times 10^{-34}$
$= 7.24 \times 10^{18}\: Hz$
Ans : (c)

edited Mar 13, 2014