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11. Dual nature of radiation and matter — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics11. Dual nature of radiation and matter1 Mark
MCQ
An electron is accelerated through a potential difference of $200$ volts. If $e/m$ for the electron be $1.6 \times {10^{11}}$ $coulomb/kg$ , the velocity acquired by the electron will be
  • ✓
    $8 \times {10^6}\,m/s$
  • B
    $8 \times {10^5}\,m/s$
  • C
    $5.9 \times {10^6}\,m/s$
  • D
    $5.9 \times {10^5}\,m/s$
✓

Answer

Correct option: A.
$8 \times {10^6}\,m/s$
a
(a) $\frac{1}{2}m{v^2} = QV$

$ \Rightarrow v = \sqrt {\frac{{2QV}}{m}} = \sqrt {2\left( {\frac{e}{m}} \right)V} $

$ \Rightarrow v = \sqrt {2 \times 1.6 \times {{10}^{11}} \times 200} = 8 \times {10^6}m/s$.

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