Figure 11. Movement of a Magnetic Field Through a Conductor

Electronic Principles
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is induced in the conductor. The emf is called a SELFINDUCED

EMF because it is induced in the conductor carrying the current.

This cmf is also referred to as COUNTER ELECTROMOTIVE FORCE

(cemf). The polarity of the counter electromotive force is in

the opposite direction to the applied voltage of the conductor.

The overall effect will be to oppose a change in current

magnitude. This effect is summarized by Lenz's law which states

that: THE INDUCED EMF IN ANY CIRCUIT IS ALWAYS IN A DIRECTION TO

OPPOSE THE EFFECT THAT PRODUCED IT.

FIGURE 11. MOVEMENT OF A MAGNETIC FIELD THROUGH A CONDUCTOR.

If the shape of the conductor is changed to form a loop, then

the electromagnetic field around each portion of the conductor

cuts across some other portion of the same conductor. This is

shown in its simplest form in figure 12 on the following page.

A length of conductor is looped so that two portions of the

conductor lie next to each other. These portions are labeled

conductor 1 and conductor 2. When the switch is closed, current

(electron flow) in the conductor produces a magnetic field

around ALL portions of the conductor. For simplicity, the

magnetic field (expanding lines of flux) is shown in a single

plane that is perpendicular to both conductors. Although the

expanding field of flux originates at