Physics Electromagnetism NUMS 2023
PMDC Verified Question 20 of 58
If a charged particle enters the magnetic field parallel, it will:
A
Deflect toward north
B
Deflect toward south
C
Move straight
D
Move in circular path
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Move straight
Concept:

The magnetic force requires a cross product. If vectors are perfectly parallel, their cross product, and therefore the resulting force, collapses to zero.

Formula:

$$ \mathbf{F} = q(\mathbf{v} \times \mathbf{B}) = qvB \sin(\theta) $$

Solution:

  • The term "parallel" defines the angle \( \theta \) between velocity and field as exactly \( 0^\circ \).


  • The sine of zero is zero (\( \sin 0^\circ = 0 \)).


  • This renders the entire magnetic force equation to \( F = 0 \).


  • Lacking any deflecting force, Newton's law dictates the particle must persist in a straight line.


Why other options are incorrect:

Options A, B, and D describe paths curved by a net transverse force, which is mathematically impossible in a parallel trajectory.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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