nguyen (ktn529) – Practice Midterm 03 – yao – (56120)
1
This
printout
should
have
18
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001
10.0points
A 1
.
11 H inductor carries a steady current
of 0
.
547 A.
When the voltage source in the
circuit is shorted out, the current disappears
in 15
.
1 ms.
What is the average induced
emf
in the
inductor during this time?
L
= 0
.
486 m
,
B
= 0
.
000192 T
,
and
μ
0
= 4
π
×
10
−
7
T
·
m
/
A
.
The magnetic field inside a long solenoid is
parenleftbigg
N
L
parenrightbigg
003
10.0points
Use Lenz’s law to answer the following ques
tion concerning the direction of induced cur
rents.
v
S
N

ε

=
L
Δ
I
Δ
t
= (1
.
11 H)
0
.
547 A
0
.
0151 s
=
40
.
2099 V
.
002
10.0points
What current is required in the windings
of a long solenoid that has 2100 turns uni
formly distributed over a length of 0
.
486 m
in
order
to
produce
a
magnetic
field
of
magnitude 0
.
000192 T at the center of the
solenoid?
The permeability of free space is
4
π
×
10
−
7
T
·
m
/
A
.
R
a
b
We introduce the following notations:
A) The direction of the induced magnetic field
within the solenoid is
•
A1 : to the left
•
A2 : to the right
•
A3 : upward
•
A4 : downward
•
A5 : into the paper
B)
The
direction
of
the
induced
current
through the resistor
R
is
•
B1 : from a through
R
to b
•
B2 : from b through
R
to a
What is correct when the bar magnet is moved
to the left?
nguyen (ktn529) – Practice Midterm 03 – yao – (56120)
2
2.
A2, B2
004
10.0points
In the arrangement shown in the figure,
the resistor is 8 Ω and a 9 T magnetic field
is directed into the paper.
The separation
between the rails is 7 m
.
An applied force
moves the bar to the right at a constant speed
of 2 m
/
s
.
m
≪
1 g
2 m
/
s
8 Ω
9 T
9 T
I
7 m
Calculate
the
applied
force
required
to
move the bar to the right at a constant speed
of 2 m
/
s
.
Assume the bar and rails have negli
gible resistance and friction. Neglect the mass
of the bar.