An EMF is induced in a conductor whenever the flux lines of a magnetic field are cut. If the magnetic field is perpendicular to the surface, the magnetic flux
passing through the area
is defined in terms of the magnetic field strength
In a uniform field
This shows B can be thought of as magnetic flux density and implies the units
(also called Weber (Wb)).
If the area A is not perpendicular to the magnetic field but at an angle %theta to it, the area facing the field is
and the flux through the area A is
illustrated below.
We can find the induced EMF E in a current loop as it moves through a magnetic field perpendicular to the field (shown as x's or tails of arrows in the diagram).
The amount of fluxcut as the coil moves a distance
is
and and this happens in a time
so we can take
where
is the speed.
Then