Increasing Current in Coil

Increasing current in a coil of wire will generate a counter emf which opposes the current. Applying the voltage law allows us to see the effect of this emf on the circuit equation. The fact that the emf always opposes the change in current is an example of Lenz's law.

The relation of this counter emf to the current is the origin of the concept of inductance. The inductance of a coil follows from Faraday's law.

Transient behavior of coil
Index

Faraday's law concepts

Inductance concepts
 
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Inductance of a Coil

Coil's reaction to increasing current

For a fixed area and changing current, Faraday's law becomes

Since the magnetic field of a solenoid is
then for a long coil the emf is approximated by
From the definition of inductance
we obtain
Inductance of a solenoid
Index

Inductance concepts

AC Circuits
 
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