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DEPARTMENT OF NATURAL SCIENCES
PHYS 1112, Exam 3
Version 1
Total Weight: 100 points
Section 1
November 22, 2013
1.
Check your examination for completeness prior to starting. There are a total of nine (9)
problems on seven (7) pages.
2.
Authorized references include your calculator with calculator handbook, and the Reference
Data Pamphlet (provided by your instructor).
3.
You will have 50 minutes to complete the examination.
4.
The total weight of the examination is 100 points.
5.
There are six (6) multiple choice and three (3) calculation problems. Work five (5) multiple
choice problems and all calculation problems. Show all work; partial credit will be given for correct
work shown.
6.
If you have any questions during the examination, see your instructor who will
be located in the classroom.
7.
Start:
Stop:
9:00 a.m.
9:50 a.m
PROBLEM
POINTS
1-6
25
7
25
8
25
9
25
TOTAL
100
PERCENTAGE
CREDIT
CIRCLE THE SINGLE BEST ANSWER FOR ALL MULTIPLE CHOICE QUESTIONS UNLESS
INSTRUCTED OTHERWISE. IN MULTIPLE CHOICE QUESTIONS WHICH REQUIRE A
CALCULATION SHOW WORK FOR PARTIAL CREDIT.
1.
A ray of light passes from air into a block of clear plastic. How does the angle of
incidence in the air compare to the angle of refraction in the plastic?
a. The two angles cannot be compared without additional information.
b. The angle of incidence is less than the angle of refraction.
(5)
c. The angle of incidence is equal to the angle of refraction.
d. The angle of incidence is greater than the angle of refraction.
2.
The “ELI the ICE man” mnemonic helps you remember that
a. Current in an inductor lags behind voltage.
b. Voltage in an inductor lags behind current.
(5)
c. Current in a resistor lags behind voltage.
d. Voltage in a resistor lags behind current.
3.
Which of the following statements are true regarding electric generators?
Check all that apply.
a. An electric generator creates a time-dependent induced voltage.
b. An electric generator is used to increase or decrease an alternating current voltage.
(5)
c. An electric generator creates a time-independent induced voltage.
d. An electric generator converts electrical energy into magnetic energy.
e. An electric generator converts mechanical energy into electrical energy.
4.
In the figure, a conducting rod is shown moving in a uniform magnetic field . Which of
the following statements are true? Check all that apply.
a. The magnitude of the potential difference in the rod is proportional to the strength
of the magnetic field.
b. An electric field is established in the rod directed from point a to point b.
(5)
c. The free charges in the rod are acted upon by a magnetic force.
d. The magnitude of the potential difference in the rod is proportional to the velocity
v of the rod.
e. The magnitude of the potential difference in the rod is inversely proportional to
the length L of the rod.
5.
A resistor, an inductor, and a capacitor are connected in series to an AC source. What is
the condition for resonance to occur?
a. The capacitive reactance must be equal to the inductive reactance.
b. The resistance must be equal to both the inductive reactance and the capacitive
reactance.
c. The resistance must be greater than the inductive reactance.
d. The inductive reactance must be greater than the capacitive reactance.
e. The capacitive reactance must be greater than the inductive reactance.
f. The resistance must be greater than the capacitive reactance.
PHYS 1112 Exam 3, Version 1
Fall 2013
3
(5)
6.
A capacitor is connected across an AC source. Which of the following graphs shows the
instantaneous current in the circuit and the instantaneous voltage across the capacitor?
(5)
This is the capacitor:
PHYS 1112 Exam 3, Version 1
Fall 2013
4
A series RLC circuit contains the following components: R = 60.0 Ω, L = 0.390 H, C =
16.0 µF, and a source with ΔVMAX = 65.0 V operating at 1050 Hz.
7.
(25)
a. Find the impedance in the circuit.
X L  2fL  (2 )(1050 Hz)(0.390 H )  2573 
XC 
1
1

 9.47 
2fC (2 )(1050 Hz)(16.0  10 6 F )
Z  R 2  ( X L  X C ) 2  2564 
b. Calculate the maximum current in the circuit.
Vm  I m Z
I m  Vm / Z  0.0253 A
c. Determine the maximum voltage across the resistor.
Vm  I m R  1.52 V
d. Determine the maximum voltage across the capacitor.
Vm  I m X C  0.240 V
e.
Determine the maximum voltage across the inductor.
Vm  I m X L  65.1 V
f.
Why can the maximum voltages add up to more than 65.0 V?
Voltages across all three elements changes out of phase with each other which allows them to
add to more than 65.0 V.
PHYS 1112 Exam 3, Version 1
Fall 2013
5
8.
A thin layer of ice n = 1.309 floats on the surface of water n=1.333 in a bucket. A ray of
light from the bottom of the bucket travels upward through the water.
a. What is the largest angle with respect to the normal that the ray can make at the
ice-water interface and still pass out into the air above the ice?
(25)
n1  1.333
n 2  1.309
n3  1.000
1.309 sin  2  1.000 sin(90.0 o )
 2  49.8 o
1.333 sin  3  1.309 sin(49.8 o )
 3  48.6 o
b.
What is this angle after the ice melts?
n1  1.333
n 2  1.000
n1 sin 1  n2 sin 2
1.333 sin 1  1.000 sin(90.0 o )
 2  48.6 o
9.
The conducting rod ab shown in the figure makes contact with metal rails ca and db. The
apparatus is in a uniform magnetic field 0.800 T, perpendicular to the plane of the figure.
(25)
PHYS 1112 Exam 3, Version 1
Fall 2013
6
a.
Find the magnitude of the emf induced in the rod when it is moving toward the
right with a speed 7.50 m/s.
  Bvl  (0.800 T )(7.50 m / s)(0.50 m)  3.00 V
b.
In what direction does the current flow in the rod?
Counterclockwise
If the resistance of the circuit abdc is 1.50 Ω (assumed to be constant), find the
magnitude of the force required to keep the rod moving to the right with a
constant speed of 7.50 m/s. You can ignore friction.
c.
I

R
 2.00 A
Fap  FB  IBl sin   (2.00 A)(0.800 T )(0.500 m) sin(90.0 o )  0.800 N
d.
Find the direction of the force required to keep the rod moving to the right with a
constant speed of 7.50 m/s.
To the right.
PHYS 1112 Exam 3, Version 1
Fall 2013
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