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4. Moving charges and magnetism — Physics STD 12 Science — Question

CBSE BoardEnglish MediumSTD 12 SciencePhysics4. Moving charges and magnetism1 Mark
MCQ
An electron accelerated through a potential difference $V$ enters a uniform transverse magnetic field and experiences a force $F$. If the accelerating potential is increased to $2V$, the electron in the same magnetic field will experience a force
  • A
    $F$
  • B
    $\frac{F}{2}$
  • ✓
    $\sqrt 2 F$
  • D
    $2F$
✓

Answer

Correct option: C.
$\sqrt 2 F$
c
$F=B q v$

But $\frac{1}{2} m v^{2}=e V$ or $v=\sqrt{\frac{2 e V}{m}}$

$\therefore F=B q \sqrt{\frac{2e v}{m}}$

$\Rightarrow F \propto \sqrt{V}$ and

$F \propto \sqrt{2 V}$

$\frac{F^{\prime}}{F}=\sqrt{2}$ or $F^{\prime}=\sqrt{2} F$

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