Physics Electromagnetism PMDC 2021
PMDC Verified Question 40 of 58
Unit of Magnetic flux
A
\( \text{Tm}^2 \)
B
Weber
C
Both A and B
D
Tesla
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Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: Both A and B
Concept:

Magnetic flux (\(\Phi\)) quantifies the total magnetic field passing perpendicularly through a given surface area.

Formula:

$$\Phi = \vec{B} \cdot \vec{A} = BA\cos\theta$$

Solution:

  • Option A (\(\text{T}\cdot\text{m}^2\)): Looking at the defining equation \(\Phi = B \cdot A\), the SI unit of magnetic flux density (\(B\)) is Tesla (\(\text{T}\)) and the unit of Area (\(A\)) is square meters (\(\text{m}^2\)), yielding \(\text{T}\cdot\text{m}^2\).
  • Option B (Weber): In the SI system, \(1\text{ T}\cdot\text{m}^2\) is given the special name Weber (Wb): $$1\text{ Wb} = 1\text{ T}\cdot\text{m}^2 = 1\text{ N}\cdot\text{m}\cdot\text{A}^{-1} = 1\text{ J}\cdot\text{A}^{-1}$$
  • Therefore, both \(\text{T}\cdot\text{m}^2\) and \(\text{Weber}\) are identical, correct SI representations of magnetic flux.
  • Option C (Both A and B) is the comprehensive correct answer.


Why other options are incorrect:

  • D (Tesla): Tesla (\(\text{T}\)) is the unit for magnetic flux density (magnetic field strength \(B\)), not magnetic flux (\(\Phi\)).

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