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Magnetic flux
Intermediate
Field passing through a surface.
Φ = BA cosθΦ = BA cosθ counts field lines through a loop; unit weber (T·m²). It changes if B, A or the angle changes.
0.5 T through 0.02 m² face-on: 10 mWb.
Flux is zero if B is parallel to the surface.
In more detail
Magnetic flux is the total magnetic field passing through a surface, Φ = BA cos θ. It is measured in webers, and it is the quantity that changes in electromagnetic induction.
Real-world uses
- Transformers depend on the flux linking primary and secondary coils.
- Magnetic flux sensors measure field through loops.
- Engineers designing coils for generators calculate the flux through each turn, which determines the induced emf.
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Frequently asked questions
What is a weber?
One tesla metre squared, the unit of magnetic flux.
Why is cos θ included?
Because only the component of field perpendicular to the surface contributes to the flux.
What does the cosine in flux mean?
It accounts for the angle between the field and the normal to the surface, so a field parallel to the surface passes no flux.
Related topics in Magnetism & Induction
Curie temperature · Electromagnets · Permanent magnets · Faraday's law · Lenz's law · Motional emf