CHAPTER 30:
Inductance, Electromagnetic Oscillations, and AC
Circuits
Responses to Questions
(
a
) For the maximum value of the mutual inductance, place the coils close together, face to
face, on
the same axis.
(
b
) For the least possible mutual inductance, place the coils with their faces perpendicular to
each
other.
2.
The magnetic field near the end of the first solenoid is less than it is in the center.
Therefore
the flux through the second coil would be less than that given by the formula, and the mutual
inductance would be lower.
3.
Yes. If two coils have mutual inductance, then they each have the capacity for self
inductance. Any coil that experiences a changing current will have a selfinductance.
4.
The energy density is greater near the center of a solenoid, where the magnetic field is
greater.
5.
To create the greatest selfinductance, bend the wire into as many loops as possible. To
create the least selfinductance, leave the wire as a straight piece of wire.
6.
(
a
) No. The time needed for the
LR
circuit to reach a given fraction of its maximum possible
current depends on the time constant,
τ
= L/R
, which is independent of the emf.
(
b
) Yes. The emf determines the maximum value of the current (
I
max
= V
0
/R
,) and therefore
will
affect the time it takes to reach a particular value of current.
A circuit with a large inductive time constant is resistant to changes in the current. When a
switch is opened, the inductor continues to force the current to flow. A large charge can
build up on the switch, and may be able to ionize a path for itself across a small air gap,
creating a spark.
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 Spring '09
 Thomas
 Inductance, Energy, Inductor, LRC, resonant frequency

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