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LECTURE 22
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for part (c) and (d) of Problem 5,
Exam II, bring your exam book
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• lecture notes
Emf induced in a moving conductor
I . The direction of the
current in the loop is:
(a) clockwise
(b) counterclockwise
II. If the conducting rod
moves to the left, the
direction of the current
in the loop is:
(a) clockwise
(b) counterclockwise
II. Calculate the magnitude of the current
through the resistor.
Exercise: Both circuit 1 and 2 are in
the same constant magnetic field B.
The current induced in circuit 1
is counterclockwise.
I. The magnetic field points
(a) into the page
(b) out of the page
II. The current in circuit 2 is
(a) clockwise
(b) Counterclockwise
III. The current in circuit 2 is
(a) larger than,
(b) Smaller than,
(c) equal to the current in circuit 1.
R
2L
v
v
L
R
Application: Electric Generator
Axle
The frame of area A and loop number N is rotated with uniform
angular velocity w. At time t=0, the angle q=0. Calculate and
sketch as a function of time
(a) the induced emf E(t) and
(b) the power P(t) dissipated in the bulb.
E(t), P(t)
Application II: Seismograph (geophone)
Seismograph
Actual reading:
Date: January 17, 1994
Place: Northridge, CA
Eddy currents
Eddy currents:
currents induced
by varying
B fields inside a
bulk metal.
Experimental evidence for eddy currents:
Finite magnetic resistance force acting
on a metal sheet when removed from field
Application: Induction-based heating
Induction technology transfers heat only to the
pan, does not transfer heat to the surrounding air.
Induced eddy currents heat the pan
Range: powerful electromagnet
Inductance
Mutual inductance
 2= M 2,1I1
dI1
E2 =  M 2,1
dt
Self- inductance
 1= L I1
dI1
E1 =  L
dt
Exercise: Label points A and B with plus
or minus signs, according to the polarity
of the self-induced emf.