Download exam2

Physics 112
Exam 2
Summer 2015
Name_________________
Physics 112
Summer 2015
Exam 2
Monday, July 13
Directions:
This 60-minute exam consists of twenty multiple-choice questions. This test is worth 20% of
your final grade. (One point is equal to 1% of the final grade.)
The questions on this test are not in order of difficulty.
You must mark all of your answers on both your test and answer sheet.
In marking the multiple choice bubble sheet use a number 2 pencil. Do not use ink. If you did
not bring a pencil, ask for one. Fill in the appropriate circles completely. If you need to change
any entry, you must completely erase your previous entry.
Carefully read each question and its five possible answers. Select one and only one answer for
each question. Choose the answer that is closest to the correct one.
When you are finished with the exam, return the bubble sheet, the exam itself, and scratch paper
that you used for the exam.
Good luck!
1
Physics 112
Exam 2
Summer 2015


21. Negative charge q is moving with velocity v in the magnetic field B as shown below (with


vectors v and B on the surface of the page). What is the direction of the magnetic force?


B
A) Parallel to v

B) Parallel to B


C) Exactly between v and B


q
D) Into the page
v
E) Out of the page
22. A positively charged particle (q = + 60 μC) moves at 2.0  10 5 m/s in a direction that is 30o to
a uniform magnetic field of 0.50 T. What is the magnetic force on the charge?
A)
B)
C)
D)
E)
1.0 N
1.5 N
2.0 N
2.5 N
3.0 N
23. An electron is moving at speed v = 800 m/s. It enters a region with uniform electric field
 

E = 400 V/m and uniform magnetic B field. Vectors E , B and v are perpendicular to each other.
The electron continues on the straight path. What is the magnitude of the magnetic field B?
A)
B)
C)
D)
E)
0.5 T
1.0 T
1.5 T
2.5 T
3.0 T
24. The force on a current-carrying wire in a magnetic field is the strongest when
A)
B)
C)
D)
E)
The current is parallel to the field lines
The current is at a 30° angle with respect to the field lines
The current is at a 45° angle with respect to the field lines
The current is at a 60° angle with respect to the field lines
The current is perpendicular to the field lines
2
Physics 112
Exam 2
Summer 2015
25. A coil of wire has 100 turns and a cross sectional area of 0.10 m2. The coil is free to rotate
and sits in a uniform 0.50 T magnetic field that points at 30° to the normal of the coil. If a 4.0A
current passes through the coil, determine the torque on the coil?
A)
B)
C)
D)
E)
2.0N  m
5.0N m
10N m
20N  m
There is no torque because the current in the coil is steady
26. A wire loop is in a uniform magnetic field. Current flows in the wire loop, as shown. What
does the loop do?
A)
B)
C)
D)
E)
Moves to the right
Moves up
Remains motionless
Rotates
Moves out of the page
27. Two long parallel wires are 4.0 cm apart. Each wire carries the current 3.0A in the same
direction. Find the magnetic field at a point that is 3.0 cm from one wire and 1.0 cm from the
other wire.
A)
B)
C)
D)
E)
4 10 5 T
6  10 5 T
4 10 5 T
6  10 7 T
zero
out of the page
out of the page
into the page
into the page
I
I
3.0 cm
1.0 cm
28. If current in each of two long parallel wires is doubled, what happened with force of
interaction between these wires?
A)
B)
C)
D)
E)
Double
Quadruple
Decrease by one-half
Decrease by one-fourth
Remain the same
3
Physics 112
Exam 2
Summer 2015
29. If current in a solenoid is doubled, what happened with the field inside the solenoid?
A)
B)
C)
D)
E)
Double
Quadruple
Decrease by one-half
Decrease by one-fourth
Remain the same
30. A bar magnet falls through a loop of wire with the north pole entering first. As the north pole
enters the wire, the induced current will be (as viewed from above):
A)
B)
C)
D)
E)
Zero
Clockwise
Counterclockwise
To top of loop
A current whose direction cannot be determined from the information given

v
S
N
31. A coil of 600 turns with area 100 cm2 is placed in a uniform magnetic field. The angle
between the direction of the field and the perpendicular to the loop is 60°. The field changes
at the rate of 0.010 T/s. What is the magnitude of induced emf in the coil?
A)
B)
C)
D)
E)
0.01 V
0.02 V
0.03 V
0.10 V
0.20 V
32. An airplane with a wing span of 50 m flies horizontally at a location where the downward
component of the Earth's magnetic field is 6.0 × 10-5 T. Find the magnitude of the induced emf
between the tips of the wings when the speed of the plane is 200 m/s.
A)
B)
C)
D)
E)
0.4 V
0.5 V
0.6 V
1.2 V
1.8 V
4
Physics 112
Exam 2
Summer 2015
33. A 6 V battery is connected to the primary coil of a transformer that is designed to convert
120 V to 240 V. What is voltage drop across the secondary coil?
A)
B)
C)
D)
E)
6V
12 V
120 V
240 V
Zero
34. What is the direction of the induced current in the circular loop due to an increasing current
that flows to the left in the straite wire as shown below?
A)
B)
C)
D)
E)
Clockwise
Counterclockwise
Alternating current
No current induced
Not enough information to answer
35. A 4.0-mH coil carries a current of 5.0 A. How much energy is stored in the coil's magnetic
field?
A)
B)
C)
D)
E)
2.0 mJ
10 mJ
20 mJ
50 mJ
80 mJ
36. After how many time constants does the current in a LR circuit reach 90% of its maximum
value?
A)
B)
C)
D)
E)
1.2
2.3
3.4
4.5
never
5
Physics 112
Exam 2
Summer 2015
37. An inductance coil operates at 240 V and 60.0 Hz. It draws 12.8 A. What is the coil’s
inductance?
A)
B)
C)
D)
E)
1.0  10 2 H
2.0  10 2 H
3.0  10 2 H
4.0  10 2 H
5.0  10 2 H
38. The amplitude of magnetic field in a sinusoidal electromagnetic wave is 4.0 µT. What is the
amplitude of the electric field in this wave?
A)
B)
C)
D)
E)
2400 V/m
1200 V/m
600 V/m
300 V/m
150 V/m
39. Unpolarized light passes through three successive ideal polarizers, each of whose axis makes
a 30° angle with the previous one. What fraction of the light intensity is transmitted?
A)
B)
C)
D)
E)
1/4
1/8
3/8
9/32
27/64
40. An electromagnetic wave in vacuum has a frequency of 1.00 MHz. What is the wavelength
of the wave?
A)
B)
C)
D)
E)
1.00 cm
3.00 cm
1.00 m
3.00 m
300 m
6
Physics 112
Exam 2
Summer 2015
Record Sheet
You may fill in this sheet with your choices, detach it and take it with you after the exam for
comparison with the posted answers
21
31
22
32
23
33
24
34
25
35
26
36
27
37
28
38
29
39
30
40
7