| A changing magnetic field will induce an
Emf in a loop of wire. The direction of that Emf is described
by Lenz's Law. This says that any Emf induced will be
in such a direction to create a magnetic field to OPPOSE
the change in magnetic flux seen through the loop. In
other words, if the magnetic field through the loop is
decreasing toward the right, the induced magnetic field
will be toward the right as well, to try to keep the magnetic
flux constant --- to try to oppose the decrease. The direction
of the current creating that field is determined by the
right hand rule. |
 |
The "jumping ring" demonstration
shows that a changing magnetic field can induce a strong
magnetic field in a conducting loop. The actual physics
using alternating current is a bit more complicated that
we can go into in Physics II, but the effect is clearly
seen as the aluminum ring is rocketed off the iron rod
when a voltage is applied to the coil. (The iron rod serves
to intensify the magnetic field created by the coil.)
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