Production of Induced EMF by Changing the Magnetic Field

The first and most direct route to producing an induced emf is by changing the magnetic field strength B itself, while the circuit's own area and orientation stay fixed. This is exactly the mechanism at work in BOTH of Faraday's original experiments (section 4.1.3): in the first experiment, the relative motion between a bar magnet and a coil changes the strength of the field linking the coil as the magnet approaches or recedes; in the second experiment, a rising or falling primary current changes the strength of the magnetic field it produces, which in turn changes the flux linked with a neighbouring secondary coil. In both cases, the coil's own area and its orientation relative to the field remain …