(2) magnetic field;
(3) relative motion between the two
a. expands; b. collapses
Inductance is the property of an electrical circuit that
a. opposes a change in voltage.
b. opposes a change in current.
c. opposes current flow.
In 1834, H.F.E. Lenz, a German physicist, formulated a law which is still the basis for explanation of the
The inducted emf in any circuit is always in a direction to oppose the effect
that produced it.
The voltage induced in a circuit by a changing current is called counter emf. When circuit current increases,
the expanding magnetic field induces an emf (counter emf) that opposes the applied voltage and the
increase in current. When circuit current decreases, the collapsing magnetic field induces a voltage of
opposite polarity which tends to maintain current flow in the same direction and to oppose a decrease in
current. The drawings below show the effect of counter emf in a d-c circuit. When the circuit is turned "on,"
the counter emf opposes the increased in current. When the circuit is turned "off", the counter emf tries to
maintain the same direction of current flow. A spark is produced as the switch is opened.
Lenz's law states that the induced emf in any circuit is always in a direction to __________________
the effect that produced ft.