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Magnetic Flux & Induction

01Magnetic Flux & Induction

Magnetic flux

This section covers magnetic flux, its dependence on magnetic flux density and area, and the significance of the surface normal.

Flux through an area

Magnetic flux, Φ\Phi, describes the magnetic field passing through a given area. When a uniform magnetic field is perpendicular to an area:

Φ=BA\Phi=BA
Symbol Quantity Unit
Φ\Phi magnetic flux weber, Wb
BB magnetic flux density T
AA area m2^2

The orientation of the area matters. The direction perpendicular to a surface is called its normal.

  • Flux is greatest when the field is parallel to the normal, so the field passes perpendicularly through the surface.
  • Flux falls to zero when the magnetic field is parallel to the plane of the surface.

Thinking in terms of the normal prevents confusion about which angle is being used.

areaAnormalB

Worked example: A rectangular area measures 0.40 m0.40\ \mathrm m by 0.73 m0.73\ \mathrm m and is perpendicular to a magnetic field of flux density 1.8×10−5 T1.8\times10^{-5}\ \mathrm T. Calculate the magnetic flux.

A=(0.40)(0.73)=0.292 m2A=(0.40)(0.73)=0.292\ \mathrm{m^2}

Φ=BA=(1.8×10−5)(0.292)\Phi=BA=(1.8\times10^{-5})(0.292)

Φ≈5.3×10−6 Wb\boxed{\Phi\approx5.3\times10^{-6}\ \mathrm{Wb}}

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