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Instructor(s):
PHYSICS DEPARTMENT
EXAM II
PHY 2005, Spring 2008
Name (print, last first):
March 24, 2008
Signature:
On my honor, I have neither given nor received unauthorized aid on this examination.
YOUR TEST NUMBER IS THE 5-DIGIT NUMBER AT THE TOP OF EACH PAGE.
(1) Code your test number on your answer sheet (use lines 76–80 on the answer sheet for the 5-digit number).
Code your name on your answer sheet. DARKEN CIRCLES COMPLETELY. Code your UFID number on your
answer sheet.
(2) Print your name on this sheet and sign it also.
(3) Do all scratch work anywhere on this exam that you like. Circle your answers on the test form. At the end of the
test, this exam printout is to be turned in. No credit will be given without both answer sheet and printout.
(4) Blacken the circle of your intended answer completely, using a #2 pencil or blue or black ink. Do not make
any stray marks or some answers may be counted as incorrect.
(5) The answers are rounded off. Choose the closest to exact. There is no penalty for guessing.
(6) Hand in the answer sheet separately.
Physical Constants:
g = 9.8 m/s2
me = 9.11 × 10−31 Kg
−27
mp = 1.67 × 10
Kg
e = 1.6 × 10−19 C
constant k in Coulomb’s Law: k = 9 × 109 Nm2 /C2
μo = 4π × 10−7 N/A2 εo = 8.85 × 10−12 C2 /Nm2
1. A sodium ion (q = +e, m = 23 × 10−27 kg) is moving with a certain speed perpendicular to a magnetic field of 0.1 T.
What must be the speed of the particle to make a circle with 0.4 m radius? (in m/s)
(1) 2.8 × 105
(2) 1.3 × 107
(3) 0.7 × 108
(4) 1.3 × 10−2
2. Two particles with the same positive charge but different velocities are
moving in a uniform magnetic field as shown in the figure. Which of
the following statements is correct? Consider only magnetic force. The
arrow indicates the velocity vector for each particle.
(1) The magnitude and the direction of the forces acting on two particles are identical.
(2) The particle 2 will experience a larger force than the particle 1.
(3) The particle 1 will experience a larger force than the particle 2.
(4) The particle 1 will make a constant speed circular motion but
the particle 2 will make a linear motion.
(5) There is no force acting on each particle.
(5) 5.35 × 106
B
v1
v2
B
1
2
B
3. An electron travels through a region of space with no acceleration. Which one of the following statements is the best
conclusion? Ignore gravitational force.
(1)
(2)
(3)
(4)
(5)
E must be zero, but B might be non-zero in that region.
E and B might both be non-zero, but they must be mutually perpendicular.
B must be zero, but E might be non-zero in that region.
E and B might both be non-zero, but they must point in opposite directions.
Both E and B must be zero in that region.
4. Two 2 m long straight wires are placed on a horizontal insulating surface. The wires run parallel to each other and are
20 cm apart as shown in the figure. 1.5 A of current is flowing
in each wire in the same direction.
What is the strength of the magnetic field at A which is located
at the mid-point between the wires? You have to consider fields
produced by both wires.
(1) 0 tesla
(2) 6 × 10−6 tesla
(3) 3 × 10−6 gauss
(4) 6 × 10−6 gauss
(5) 1.5 × 10−6 tesla
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5. Refer to above question. What kind of forces do the wires experience?
(1)
(2)
(3)
(4)
(5)
attractive
repulsive
along the current direction
out of the page
into the page
6. A circular loop with a 0.1 m2 cross-section is placed in the presence of
a uniform magnetic field of 1.2 T as shown in the figure. The field is
dropped to 0.4 T in 2 s. What is the change in magnetic flux threading
through the loop? What is the direction of the induced current when
you look down the loop from above?
(1)
(2)
(3)
(4)
(5)
−0.061 Tm2 , counterclockwise
+0.08 Tm2 , counterclockwise
+0.061 Tm2 , clockwise
−0.08 Tm2 , clockwise
−0.051 Tm2 , clockwise
7. Which one of the following statements concerning permanent magnets is false?
(1)
(2)
(3)
(4)
(5)
When a permanent magnet is cut in half, one piece will be a north pole and the other piece will be a south pole.
The north pole of a permanent magnet is attracted to a south pole.
All permanent magnets are surrounded by a magnetic field.
The direction of a magnetic field is indicated by the north pole of a compass.
Magnetic field lines outside a permanent magnet originate from the north pole and end on the south pole.
8. A 3 m long straight conducting wire is moving sideways with a constant speed perpendicular to a magnetic field of B =
1.5 T. The electric potential induced across the wire is 9 V. What is the speed of the moving wire? (in m/s)
(1) 2
(2) 9
(3) 3
(4) 0.5
(5) 6
9. A single circular loop of an AC generator is rotating with a constant speed. The following figure shows the several
consecutive positions of the coil relative to the magnetic field during the rotation. The polarity of the induced EMF
changes between
. The small triangle on the loop indicates the top of the loop.
(1) (b) and (c)
(2) (d) and (e)
(3) (a) and (b)
(4) (c) and (d)
(5) none
10. An ideal transformer has a 100 turn-primary coil. When 100 V AC is applied to the secondary coil, a 1 V AC signal was
detected at the primary coil. How many turns does the secondary coil have?
(1) 10,000
(2) 1
(3) 1,000
(4) 10
(5) 100
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11. An electron is injected from left to right into a uniform magnetic field
region (B = 0.5 T) directed vertically downward. The speed of electron
is 1 × 106 m/s. What is the direction and magnitude of the force on
the electron?
(1) out of the page, 8 × 10−14 N
(2) into the page, 5 × 105 N
(3) out of the page, 1.6 × 10−13 N
(4) into the page, 8 × 10−14 N
(5) to the right, 1.6 × 10−14 N
12. A single conducting loop with an area of 2.0 m2 rotates in a uniform magnetic field so that the induced EMF has a sinusoidal time
dependence as shown. Which is the most accurate mathematical
representation of the induced EMF?
(1)
(2)
(3)
(4)
(5)
7.5sin(1.26t)
7.5sin(5t)
7.5sin(31.4t)
15sin(6.28t)
15cos(31.4t)
THE FOLLOWING QUESTIONS, NUMBERED IN THE ORDER OF THEIR APPEARANCE ON THE ABOVE LIST,
HAVE BEEN FLAGGED AS CONTINUATION QUESTIONS: 5