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Physics 4322
Homework Set 3
January 31, 2012
Due: Tuesday, February 7, 2012
1. A square loop of wire is placed in a magnetic field
B
as shown.
The
wire is released from rest and allowed to fall under the action of gravity.
(a) Find an expression for the velocity
v
as function of time
t
.
(b) How
long a time is required to reach 90% of terminal velocity?
(c) Describe the
motion of the loop if a tiny section is removed so as to break the complete
circuit.
2. A long solenoid with radius
a
and
n
turns per unit length carries a time
dependent current
I
(
t
) in the
φ
^
direction.
Find the electric field
E
at a distance
s
from the axis
inside and outside the solenoid in the quasistatic approximation.
3. A square loop having side
a
and resistance
R
lies a distance s
from an infinite straight wire that carries current
I
(
t
) = (1 –
α
t
)
I
for 0
≤
t
≤
1/
and 0 for all other times.
(a) In what direction is
the current in the square loop?
(b) What total charge passes
through a given point during the time the current exists?
4. Find the selfinductance per unit length of a long solenoid having radius
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 LOWELLWOOD
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