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Dr. Jie Zou

PHY 1361

1

Chapter 32

Inductance

Dr. Jie Zou

PHY 1361

2

Outline

Self-inductance (32.1)
Mutual induction (32.4)
RL circuits (32.2)
Energy in a magnetic field (32.3)
Oscillations in an LC circuit (32.5)
The RLC circuit (32.6, 33.5)

Dr. Jie Zou

PHY 1361

3

Self inductance

Self induction: the changing flux through the circuit and the resultant induced
emf arise from the circuit itself. The emf L set up in this case
is called a self-induced emf.


L
= -L(dI/dt)
L = - L/(dI/dt):
Inductance is a measure of the opposition to a change in current.

Inductance of an N-turn coil: L = NB/I; SI unit: henry
(H).

Due to self-induction, the current in the circuit does not jump
from zero to its maximum value instantaneously when the switch is thrown
closed.

Dr. Jie Zou

PHY 1361

4

Mutual induction

Mutual induction: Very often, the magnetic flux through the area enclosed
by a circuit varies with time because of time-varying currents in nearby
circuits. This condition induces an emf through a process known as mutual
induction.
An application: An electric toothbrush
uses the mutual induction of solenoids as part of its battery-charging
system.

Dr. Jie Zou

PHY 1361

5

RL circuits

An inductor: A circuit element that has a large self-inductance is
called an inductor.