A charged particle enters a magnetic field with velocity v at an angle \( \theta \) with the field and experiences a magnetic force. The kinetic energy of the particle
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → is not affected by magnetic force
The magnetic force on a moving charge is always perpendicular to its velocity.
\( \displaystyle \vec{F} = q\,\vec{v}\times\vec{B} \;\Rightarrow\; \vec{F}\cdot\vec{v} = 0 \)
So the force does no work on the particle. It changes only the direction of the velocity, not its magnitude, so the speed and the kinetic energy stay constant for every angle \( \theta \).
NCERT (2026-27):
Motion in a Magnetic Field – “… In the case of motion of a charge in a magnetic field, the magnetic force is perpendicular to the velocity of the particle. So no work is done and no change in the magnitude of the velocity is produced (though the direction of momentum may be changed).”