Download Exam 2

Version A Page 1 of 7
-
‘H
Spring 2008
Do NOT open out the exam until instructed to do so!
Name:________________ UIN:______
Signature:_____________________ E-mail:________
Section Number:
Section
Recitation/Lab TA
525
T2:20-5:lOpm
526
T 3:55-6:45pm Samantha Hoffmann
527
T 5:30-8:2Opm
PankajJha
Dan Xie
Version A Page 3 of 7
Problem 1 (20 points):
You have four 4.00 tF capacitors. They are initially uncharged and then connected with a battery (Vab
=
+28.0 V). Calculate the charge on C
4 and the potential
2
C
1
C
difference across C
.
4
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c
Va
—
Vb
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Version A Page 4 of 7
Problem 2 (20 points):
140 0 fl
35 0 1
The fire shows a circuit that you desi in PHYS 202 lab. You ar
41
about to measure the currents I, I, and 13.
I 12
(a) (10 pts) Write down a set of equations using Kirchhoff s junctlo
210
and loop rules. Indicate clearly the loop(s) for the ioop rule.
‘2 0
(b) (10 pts) Find those currents.
V
-
3
I—(io)÷(s)’
L
57
5T0
2_(i*o)I (2i°)i*5Q
0
—2
—.
I
fMa
3
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—
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—
—cv
I
210
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i
r
—
3S0 i
-
21
13
_oi +2)013=0
4
—°
I,
0 Ii
7 J19
3513
-
13
—7•
(j
12 =
a 3A +
a. .2 A
=:{. Ai 0
=
r
V
Version A Page 5 of 7
Problem 3 (20 points):
In PHYS 202 lecture, you learned the magnetic force on a current-carrying wire. This motivates you to design a
“magnetic balance” to weigh an object. The object’s mass m to be
1, 5.00 fI
measured is hung from the center of the horizontal bar, which is in a
uniform magnetic field of 1.50 T directed into the plane of the figure.
The bar is 50.0 cm long and is made of extremely lightweight material
with very small resistance. The battery voltage can be adjusted to vary
the current in the circuit.
(a) Which point, a or b, should be the positive terminal of the
x x x x
x x x
battery?
(b) You find the balance when the battery voltage is 125 V. Find the
m
mass of the object?
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(25A)(o5O)(l .50T)
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R.
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=25A
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Fm
i:
Version A Page 7 of 7
Problem 5 (20 points):
In a PHYS 202 lab, you are going to characterize the time response of
the circuit (C = 100 V, R
0 = 10.0 2, R = 40.0 1, andL = 200 mH). See
the figure. Both switches S
1 and S
2 are initially open.
(a) (10 pts) Find the current through R
0 just after Si is closed. Sketch
the current on R
0 as a function of time.
(b) (5 pts) Find the current through
resistor after Si has been
closed a long time;
(c) (5 pts) Find the current through R (**not** Ro) right after S is
re-opened in part (b) and S
2 is simultaneously closed.
-
(a)
Si
R
1?o
a
L
C
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