Question

When the charged particle is moving with velocity in a direction perpendicular to the uniform magnetic field, then there is no change in its kinetic energ,v even if its momentum changes."?

Answer 1

Here the momentum is subjected to direction of velocity as it is a vector quantity while kinetic energy is a scalar quantity.

In a uniform magnetic field when a particle enters perpendicularly it starts moving in a circular direction and so its velocity keeps on changing and thus momentum keeps on changing. Since, it is in uniform circular motion there is no change in magnitude of velocity and thus kinetic energy remains constant.

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