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Class 12 › Physics › Moving Charges and Magnetism
CBSE2021Class Class 12 · Physics2 Marks · Short✅ Verified
A charged particle of mass $m$ and charge $q$ travels on a circular path of radius $r$ perpendicular to a magnetic field $B$. Write the expression for the time taken by the particle to complete one revolution.
✅ Answer & Solution
Radius of circular path: $r = mv/(qB)$, so $v = qBr/m$.
Time period:
$$T = \frac{2\pi r}{v} = \frac{2\pi r}{qBr/m} = \frac{2\pi m}{qB}$$
The time period is independent of the speed $v$ and radius $r$ — this is the cyclotron principle.
