What is the unit of magnetic flux?

Question

Examoogle · Accepted Answer

Weber

Explanation: Magnetic flux (represented by the symbol \Phi) is a measure of the quantity of magnetism, taking into account the strength and the extent of a magnetic field. Its SI unit is the Weber (Wb), named after the German physicist Wilhelm Eduard Weber.

Working Principle: Magnetic flux is defined as the surface integral of the normal component of the magnetic flux density (B) over a surface area (A). Mechanically, it represents the total number of magnetic field lines passing through a given surface. According to Faraday's law, a change in magnetic flux over time induces an electromotive force (EMF) in a conductive loop.

Key Formulas: $\Phi = \int B \cdot dA$ — Total magnetic flux through an area; $1 	ext{ Wb} = 1 	ext{ Volt-second}$ — Relationship between flux and induced EMF

Key Points: One Weber is defined as the magnetic flux that, when changing at a rate of one Weber per second, induces an EMF of one volt in a single-turn circuit.; Magnetic flux density (B) is measured in Tesla (T), where $1 	ext{ T} = 1 	ext{ Wb/m}^2$.; It is a scalar quantity, despite being associated with vector fields.

Advantages: Provides a simple quantification of magnetic field interaction with circuitry.; Essential for calculating transformer and motor performance parameters.

Disadvantages: Cannot be measured directly; typically measured via induced voltage (fluxmeters).; Sensitive to the orientation of the surface relative to the field lines.

Applications: Design of electromagnetic induction devices (transformers, inductors).; Used in Hall-effect sensors and magnetic recording media.

Additional Info: Option B (Henry) is the unit of Inductance.. Option C (Ampere/metre) is the unit of Magnetic Field Strength (H).. Option D (Ampere-turn/weber) is the unit of Reluctance.

Answer: A is correct — The SI unit of magnetic flux is the Weber (Wb).

Exam Tip: Always distinguish between flux ($\Phi$, Weber) and flux density ($B$, Tesla) to avoid common calculation errors in machine design problems.

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