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A particle having mass M and charge Q moves with speed v in a uniform magnetic field B applied perpendicular to its velocity, so that it traces a circle of radius R. The total work done by the magnetic field during one complete revolution is

1. (Mv²/R) 2πR
2. zero
3. BQ2πR
4. BQv2πR

Correct answer: zero

Solution

The work done by a magnetic field on a charged particle is always zero because the magnetic force acts perpendicular to the velocity of the particle, resulting in no displacement in the direction of the force.

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