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STD 12 - 4. Moving charges and magnetism — JEE STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceJEESTD 12 - 4. Moving charges and magnetism4 Marks
MCQ
An electron and a proton enter a magnetic field perpendicularly. Both have same kinetic energy. Which of the following is true
  • A
    Trajectory of electron is less curved
  • ✓
    Trajectory of proton is less curved
  • C
    Both trajectories are equally curved
  • D
    Both move on straight-line path
✓

Answer

Correct option: B.
Trajectory of proton is less curved
b
(b) We have $qvB = \frac{{m{v^2}}}{r}$ or $r = \frac{{mv}}{{qB}} = \frac{{\sqrt {2mK} }}{{qB}}$
For same kinetic energy $K$, we have $r \propto \sqrt m $
Hence path of proton will have larger $r$ and is therefore less curved.

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