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PHYS1200
PHYSICS II
SPRING 2006
Class 9 Activity: Faraday’s Law and Inductance
SOLUTION
Faraday’s law is generally stated as
∫
Φ

=
⋅
dt
d
s
d
E
B
, although we initially used it as
1.
State in your own words what this new formulation of Faraday’s law means.
A changing magnetic field produces an electric field.
2.
A long solenoid has 200 turns per centimeter and a of radius 15 cm. It carries a current that
varies according to the equation
i
sol
=
3
t
+
t
2
,
where
i
is in amperes and
t
is in seconds. Find
the strength of the magnetic field in the solenoid as a function of time.
T
)
3
)(
10
51
.
2
(
T
)
3
)(
10
8
(
)
3
)(
20000
)(
H/m
10
4
(
)
3
(
2
2
2
3
2
7
2
0
0
t
t
B
t
t
t
t
t
t
n
ni
B
+
×
=
+
×
=
+
×
=
+
=
=



π
π
μ
μ
where t is in seconds
.
3.
At
t
= 2 s, find the flux through a circle of radius 7.0 cm, centered on the axis of the solenoid.
Wb
10
87
.
3
)
m
07
.
0
(
)
2
2
3
)(
10
51
.
2
(
)
3
)(
10
51
.
2
(
3
2
2
2
2
2
2
2



×
=
+
×
×
=
+
×
=
=
Φ
π
π
π
r
t
t
r
B
B
4.
At
t
= 2 s, find the rate of change of flux through a circle of radius 7.0 cm, centered on the
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 Spring '06
 Stoler
 Physics, Inductance

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