MCQ
If a voltage applied to an $X$ - ray tube is increased to $1.5$ times the minimum wavelength $({\lambda _{\min }})$ of an $X$ - ray continuous spectrum shifts by $\Delta \lambda = 26\,pm$. The initial voltage applied to the tube is
  • A
    $\approx  10\, kV$
  • $\approx  16\, kV$
  • C
    $\approx  50\, kV$
  • D
    $\approx  75\, kV$

Answer

Correct option: B.
$\approx  16\, kV$
b
(b) ${\lambda _{\min }} = \frac{{hc}}{{eV}}$ $⇒$ ${\lambda _1} = \frac{{hc}}{{e{V_1}}}$and ${\lambda _2} = \frac{{hc}}{{e{V_2}}}$
$\therefore$ $\Delta \lambda = {\lambda _2} - {\lambda _1} = \frac{{hc}}{e}\left[ {\frac{1}{{{V_2}}} - \frac{1}{{{V_1}}}} \right]$. Given $V_2\, = 1.5\, V_1$
on solving we get $V_1\, =\, 16000\, volt \, = \,16\, kV$.

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