20.5.1—Magnetic flux as the product of the magnetic flux density and the

Magnetic flux through a surface is Φ=BA cosθ, where θ is the angle between field and the surface normal; units are webers.

Use the component of B perpendicular to the area and state the surface orientation.

A 0.20 T field through 0.50 m² perpendicular surface gives 0.10 Wb.

Flux is not simply B times any projected length, and it is zero when the field lies entirely in the plane of the surface.