Class JEE Physics ALL Q #1176
KNOWLEDGE BASED
APPLY
4 Marks 2026 JEE Main 2026 (Online) 21st January Morning Shift MCQ SINGLE
An ideal solenoid is kept with its axis vertical. A current $I_{0}$ is flowing in the solenoid. A charge q is thrown vertically downward inside the solenoid. The acceleration of the charged particle is:
(A) $g$ downward
(B) $g$ upward
(C) Zero
(D) Depends on current $I_{0}$
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Step-by-Step Solution

  1. The magnetic field inside an ideal solenoid is along its axis.
  2. The charge q is thrown vertically downward, which is along the axis of the solenoid.
  3. The magnetic force on a moving charge is given by $\vec{F} = q(\vec{v} \times \vec{B})$.
  4. Since the velocity $\vec{v}$ of the charge is parallel to the magnetic field $\vec{B}$ inside the solenoid, the cross product $\vec{v} \times \vec{B} = 0$.
  5. Therefore, the magnetic force on the charge is zero.
  6. The only force acting on the charge is gravity, which causes an acceleration of $g$ downward.

Correct Answer: $g$ downward

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Pedagogical Audit
Bloom's Analysis: This is an APPLY question because it requires the student to apply the concepts of magnetic force on a moving charge within a solenoid to determine the acceleration.
Knowledge Dimension: CONCEPTUAL
Justification: The question tests the understanding of the magnetic field inside a solenoid and how it affects a moving charge. It requires applying the Lorentz force law in a specific context.
Syllabus Audit: In the context of JEE, this is classified as KNOWLEDGE. It directly relates to the concepts taught in electromagnetism, specifically the magnetic field due to a solenoid and the force on a moving charge.

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