HOMEWORK 7:
SOLUTIONS
Q25.5: ANSWER: no current is induced, because magnetic flux through the ring is zero.
29.1.
I
DENTIFY
:
Altering the orientation of a coil relative to a magnetic field changes the magnetic flux through the coil.
This change then induces an emf in the coil.
S
ET
U
P
:
The flux through a coil of
N
turns is
Φ
=
NBA
cos
φ
, and by Faraday’s law the magnitude of the induced
emf is =
d
Φ
/dt
.
E
XECUTE
:
(a)
∆Φ
=
NBA
= (50)(1.20 T)(0.250 m)(0.300 m) = 4.50 Wb
(b)
=
d
Φ
/dt =
(4.50 Wb)/(0.222 s) = 20.3 V
29.5.
I
DENTIFY
:
Apply Faraday’s law.
S
ET
U
P
:
Let +
z
be the positive direction for. Therefore, the initial flux is positive and the final flux is zero.
E
XECUTE
:
(a)
and
(b)
Since is positive and is toward us, the induced current is counterclockwise.
E
VALUATE
:
The shorter the removal time, the larger the average induced emf.
29.7.
I
DENTIFY
:
Calculate the flux through the loop and apply Faraday’s law.
S
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 Fall '05
 Ogilvie
 Current, Work, Flux, Magnetic Field, Faraday, long straight wire

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