(1) When a magnetic diaphragm is placed near the bar magnet, as in A, and its range of motion is limited
suitably, it will be attracted to the magnet without actually touching it. The magnet exerts a permanent pull on the
diaphragm. If a coil is wound around the magnet as in B, C, and D, and current is caused to flow in the coil, the pull on
the diaphragm will be increased or decreased, depending on the direction and magnitude of the current. If the current in
the coil is a sinewave alternating current, it varies the strength of the magnetic field accordingly.
FIGURE 15. Operation of Magnetic