AC1 Fundamentals Unit 3 – Inductance
UNIT 3 – INDUCTANCE
UNIT OBJECTIVE
At the completion of this unit, you will be able to describe the effect of inductance on a circuit by
using an oscilloscope.
UNIT FUNDAMENTALS
The property of a conductor that opposes a change in current flow is inductance (L)
The magnetic field surrounding a conductor produces an opposing electromotive force (emf) in
response to a changing current. This opposing emf is called counter electromotive force (cemf)
The amount of cemf produced by a conductor depends on the rate at which the current changes
and on the amount of inductance. The frequency of the applied ac current is the rate of change.
The higher the frequency, the more cemf produced.
The measure of inductance depends largely upon how well the magnetic field surrounding the
conductor is concentrated. A higher concentration results in a higher, more measurable amount
of inductance.
A straight piece of wire has its magnetic field spread over a large area (less concentration).
However, if we were to wind the wire into a coil, the magnetic field would then be concentrated
into a much smaller area (greater concentration).
Because of its inductive properties, the coil is called an inductor.
The figure shows the symbol for an inductor as shown on a schematic. Inductors are usually
labeled with the capital letter L.
The henry (H) is the unit of measure for inductance. An inductor measuring one henry produces
one volt of cemf when one ampere of ac current at one hertz is applied to it. For most
applications, however, inductors are in the millihenry (mH) and microhenry (μ H) ranges.
The lower the total inductance, the higher the value of circuit current.
The higher the total inductance, the lower the value of circuit current.