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Electron, Photon, Photo-electric Effect and X-Rays — JEE physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 ScienceJEE physicsElectron, Photon, Photo-electric Effect and X-Rays1 Mark
MCQ
An electron is accelerated through a potential difference of $1000$ volts. Its velocity is nearly
  • A
    $3.8 \times 10^7 \mathrm{~m} / \mathrm{s}$
  • B
    $1.9 \times 10^6 \mathrm{~m} / \mathrm{s}$
  • ✓
    $1.9 \times 10^7 \mathrm{~m} / \mathrm{s}$
  • D
    $5.7 \times 10^7 \mathrm{~m} / \mathrm{s}$
✓

Answer

Correct option: C.
$1.9 \times 10^7 \mathrm{~m} / \mathrm{s}$
(c) If the voltage given is $V$, then the energy of electron
$ \frac{1}{2} m v^2=e V \Rightarrow v=\sqrt{\frac{2 e V}{m}}$
$ =\sqrt{\frac{2 \times 1.6 \times 10^{-19} \times 1000}{9.1 \times 10^{-31}}}$
$=1.875 \times 10^7 \approx 1.9 \times 10^7 \mathrm{~m} / \mathrm{s}$

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