Table 34-1. Curie temperatures for ferromagnetic elements.Element Curie temperature (ıC)
Iron 770
Cobalt 1115
Nickel 354
Gadolinium 20
Dysprosium 18834.6 Eddy Currents
A metal like aluminum is not ferromagnetic, so a sample of it cannot be picked up with a magnet the way
iron can. However, it can still be influenced by a magnetic field.
Suppose we put a piece of aluminum at the end of a light rod, so that it forms the bob of a pendulum. If
this pendulum is allowed to swing back and forth in the presence of an external magnetic field, something
surprising happens: the motion will be strongly damped and the pendulum will quickly stop swinging.
What’s happening is that as the aluminum metal moves through the magnetic field, electric currents called
eddy currentsare induced in the aluminum; those electric currents in turn produce a magnetic field of their
own, in a direction that opposes the external magnetic field. The interaction of the external and induced
magnetic fields produces the observed damping motion.