The magnitude induced EMF through a loop of conducting material is equal to the magnitude of the time derivative rate of change of the magnetic flux through that loop.
The polarity of the induced EMF is such that oppose the changes/current that causes it.
Magnetic Field Strength
Magnetic Field Strength is defined as the force on one metre of wire carrying a current of one amp at right angles to the magnetic field. Magnetic Field Strength is also called flux density and is measured in teslas, T.