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When a charged particle moves perpendicular to a magnetic field, then which statement is correct: a) Its momentum remains constant b) Its kinetic energy remains constant c) Its velocity remains constant

When a charged particle moves perpendicular to a magnetic field, then which statement is correct: a) Its momentum remains constant b) Its kinetic energy remains constant c) Its velocity remains constant Correct Answer Only b is correct

CONCEPT:

  • Lorentz force: It is defined as the force exerted on a charged particle q moving with velocity v through an electric field E and magnetic field B. The entire electromagnetic force on the charged particle is called the Lorentz force and is given by

​⇒ FL = qE + qvBsinθ 

  • A charged particle experiences a force when it moves in a magnetic field.

​⇒ F = qvBsinθ

Where, F =  force due to magnetic field, q = magnitude of charge, v = velocity of charge, B = magnetic field and θ = angle between v and B

  • When the velocity of a charged particle is perpendicular to a magnetic field, it describes a circle and the force on the charged particle is given as,

​⇒ F = qvB

EXPLANATION:

  • When the velocity of a charged particle is perpendicular to a magnetic field, it describes a circle and the force on the charged particle is given as,

​⇒ F = qvB

  • This force will act towards the center.
  • In a circular motion, the direction of motion continuously changes, so the velocity and momentum also change continuously.
  • The above force acts towards the center, so there will be no torque on the charged particle and its speed will remain constant, so the kinetic energy of the particle also remains constant.
  • Hence, option 2 is correct.

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