Picture 16
Basic Properties of Inductors
Learning Goal:
To understand the units of inductance, the potential energy stored in an inductor, and
some of the consequences of having inductance in a circuit.
After batteries, resistors, and capacitors, the most common elements in circuits are inductors. Inductors
usually look like tightly wound coils of fine wire. Unlike capacitors, which produce a physical break in
the circuit between the capacitor plates, the wire of an inductor provides an unbroken continuous path in
which current can flow. When the current in a circuit is constant, an inductor acts essentially like a short
circuit (i.e., a zero-resistance path). In reality, there is always at least a small amount of resistance in the
windings of an inductor, a fact that is usually neglected in introductory discussions.
Recall that current flowing through a wire generates a magnetic field in the vicinity of the wire. If the
wire is coiled , such as in a solenoid or an inductor, the magnetic field is strongest within the coil parallel
to its axis. The magnetic field associated with current flowing through an inductor takes time to create,
and time to eliminate when the current is turned off. When the current changes, an EMF is generated in
the inductor, according to Faraday's law, that opposes the change in current flow. Thus inductors provide
electrical inertia to a circuit by reducing the rapidity of change in the current flow.
Inductance is usually denoted by
and is measured in SI units of henries (also written henrys, and
abbreviated
), named after Joseph Henry, a contemporary of Michael Faraday. The EMF
produced
in a coil with inductance
is, according to Faraday's law, given by
.
Here
characterizes the rate at which the current
through the inductor is changing with time
.
Part A
Based on the equation given in the introduction, what are the units of inductance
in terms of the
units of
,
, and
(respectively volts
, seconds
, and amperes
)?
ANSWER: