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NEET PHYSICSMOVING CHARGES AND MAGNETISMEasy

Question

A beam of electrons passes un-deflected through mutually perpendicular electric and magnetic fields. Where do the electrons move if the electric field is switched off and the same magnetic field is maintained?

A

in an elliptical orbit.

B

in a circular orbit.

C

along a parabolic path.

D

along a straight line.

Step-by-Step Solution

  1. Initial State (Undeflected): When the electron beam passes undeflected, the electric force (FE=qEF_E = qE) balances the magnetic force (FB=qvBF_B = qvB). This implies the velocity vector v⃗\vec{v}, electric field E⃗\vec{E}, and magnetic field B⃗\vec{B} are mutually perpendicular.
  2. Final State (E switched off): When the electric field is removed, only the magnetic force acts on the electrons: F⃗=q(v⃗×B⃗)\vec{F} = q(\vec{v} \times \vec{B}).
  3. Resulting Motion: Since the velocity v⃗\vec{v} is perpendicular to the magnetic field B⃗\vec{B}, the magnetic force acts as a centripetal force (F=qvBF = qvB), perpendicular to both v⃗\vec{v} and B⃗\vec{B} at all instants. This causes the electrons to move in a uniform circular orbit .

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from MOVING CHARGES AND MAGNETISM. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSMOVING CHARGES AND MAGNETISMelectronspassesundeflectedthroughmutually

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