1
Review:
302 SelfInductance
Conceptual Example 304: Direction of emf in inductor.
Current passes through a coil from left to right as shown. (a) If
the current is increasing with time, in which direction is the
induced emf? (b) If the current is decreasing in time, what then is
the direction of the induced emf?
Physics 208N004 Lecture #23
– 16 March 2011
Chapter 30: 4 – Magnetic Energy, RL Circuits
302 SelfInductance
Example 305: Coaxial cable inductance.
Determine the inductance per unit length
of a coaxial cable whose inner conductor
has a radius
r
1
and the outer conductor
has a radius
r
2
. Assume the conductors
are thin hollow tubes so there is no
magnetic field within the inner conductor,
and the magnetic field inside both thin
conductors can be ignored. The
conductors carry equal currents
I
in
opposite directions.
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Just as we saw that energy can be stored in an electric
field, energy can be stored in a magnetic field as well, in
an inductor, for example.
Analysis shows that the energy density of the field is
given by
303 Energy Stored in a Magnetic Field
We find the mutual inductance of the inner loop.
If we assume the
outer solenoid is carrying current
then the magnetic field inside the
outer solenoid is
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 Spring '09
 GEORGE
 Magnetic Field, Inductor, RL circuit, Faraday's law of induction, 304 LR Circuits

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