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Class 12 › Physics › Moving Charges and Magnetism
CBSE2019Class Class 12 · Physics2 Marks · Short✅ Verified
A magnetic field that varies in magnitude from point to point but has a constant direction (east to west) is set up in a chamber. A charged particle enters the chamber and travels undeflected along a straight path with constant speed. What can you say about the direction of initial velocity of the particle?
✅ Answer & Solution
For the particle to be undeflected, the magnetic force must be zero.
Magnetic force: $F = qvB\sin\theta$
$F = 0$ when $\sin\theta = 0$, i.e., $\theta = 0°$ or $180°$.
This means $\vec{v} \parallel \vec{B}$.
Hence the initial velocity of the particle must be directed along the magnetic field direction, i.e., along the east-west direction (either towards east or towards west).
