A charged particle moves through a magnetic field perpendicular to its direction. Then

kinetic energy changes but the momentum is constant
the momentum changes but the kinetic energy is constant
both momentum and kinetic energy of the particle are not constant
both momentum and kinetic energy of the particle are constant

Correct answer: the momentum changes but the kinetic energy is constant

Solution

When a charged particle moves through a magnetic field perpendicular to its velocity, the magnetic force acts as a centripetal force, changing the direction of the particle's momentum without altering its speed. Since the speed remains constant, the kinetic energy, which depends on speed, also remains constant.

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