Physics · Moving Charges and Magnetic Field

JEE Main 2025 — 24 January, Evening Shift — Question 49

Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason(R). Assertion (A) : A electron in a certain region of uniform magnetic field is moving with constant velocity in a straight line path.

Reason (A) : The magnetic field in that region is along the direction of velocity of the electron.

In the light of the above statements, choose the correct answer from the options given below :

Option A:
(A) is false but ( R ) is true
Option B:
Both (A) and (R) are true and (R) is the correct explanation of (A)
Option C:
Both (A) and (R) are true but ( R ) is NOT the correct explanation of (A)
Option D:
(A) is true but ( R ) is false
Correct

Answer: D

Step-by-step solution

$\overline{\mathrm{F}}=\mathrm{q}(\overline{\mathrm{v}} \times \overline{\mathrm{B}})$ $\overline{\mathrm{F}}=0$ $\overline{\mathrm{V}} \| \overline{\mathrm{B}}$ $\theta=0$ or 180

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Exam: JEE Main 2025
Paper: 24 January, Evening Shift
Subject: Physics
Chapter: Moving Charges and Magnetic Field
Topic: Motion of Charged Particles in Combined Electric and Magnetic Fields

Answer: D

Step-by-step solution

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