Lesson 2 of 10 · 5 min
Magnetic flux
NCERT §6.3
Arjun's pickup coil has 200 turns, each of area 2 × 10⁻³ m², and sits in a field of 0.05 T. How much field passes through it, and why does turning the coil change the answer?
The lesson in notes
In short
For a flat area A in a uniform field B, the magnetic flux is ΦB = B·A = BA cos θ, where θ is the angle between B and the area vector A (the normal to the surface).
For a curved surface or a field that varies from place to place, split the surface into small elements dA and add B·dA over all of them.
Flux is a scalar. Its SI unit is the weber (Wb), equal to T m².
Flux is largest, BA, when the field is along the normal (θ = 0°), zero when the field lies in the plane of the surface (θ = 90°), and −BA when the surface is flipped (θ = 180°).
Flux can therefore be changed in three ways: change B, change the area A, or change the angle θ.