Induction of Magnetic Fields
Study Guide for Section 33.1
Just as a changing magnetic field can induce an electric field, a changing electric field can induce
a magnetic field. This induced field obeys the following equation:
* closed B † . L œ .! %!
. FI
.>
loop
This equation is similar to Ampère's law, except that %!
. FI
has been substituted in for the
.>
current. This quantity is known as displacement current:
M. œ % !
. FI
.>
Displacement current is measured in amps (A), just like real current. However, displacement
current is not actual current, it is just a changing electric field. We only think of it as current
because it produces the same sort of magnetic field. For example, the magnetic field at a
distance < from a displacement current M. is given by the formula
F œ
.! M.
#1 <
This section pays particular attention to the displacement current between the two plates of a
capacitor. The primary thing to know about this is that the displacement current between the
plates of a capacitor is equal to the current into and out of the capacitor.
Problems: Chapter 33 # 3, 78
Answers: 78.
M. œ #% A;
F œ $# µT