Force on a particle moving with velocity v in a magnetic field B is F = q (v × B).

If angle between v and B is either zero or 180°, then value of F will be zero.
If angle between v and B is 90°, then value of F will be maximum.
The cross product of v and B will be zero.
All of the above

Correct answer: If angle between v and B is either zero or 180°, then value of F will be zero.

Solution

The magnetic force on a charged particle is given by F = q(v × B), where the magnitude of the force is F = qvBsinθ. If the angle θ between v and B is 0° or 180°, sinθ = 0, so F = 0. Thus, option A is correct.

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