Physics 25 Examination 3 March 28, 2012 Dr. Alward
1.A long, straight wire carries a 6.0-A current that is directed in the positive x direction.
When a uniform magnetic field is applied perpendicular to a 3.0-m segment of the wire,
the magnetic force on the segment is 0.36 N, directed in the negative y direction, as
shown. What are the magnitude and direction of the magnetic field?
A)
B)
C)
D)
E)
0.020 T, out of the paper
0.020 T, into the paper
0.060 T, out of the paper
0.060 T, into the paper
None of these
A)
B)
C)
D)
E)
2.An object is 1.0 m in front of a mirror. A virtual image is formed 10.0 m behind the
mirror. What is the radius of curvature of the mirror?
0.56 m
1.1 m
2.2 m
4.4 m
None of these
A)
B)
C)
D)
E)
3.A concave mirror has a radius of curvature of 20 cm. For which one of the following
object distances will the image be real, inverted and smaller than the object?
5 cm
10 cm
15 cm
25 cm
None of these
Use the following to answer questions 4-5:
A portion of an electrical circuit lies between the poles of a magnet whose magnetic field
strength is 2.0 T. The arrows in the drawing show the direction of the magnetic field. The length
of the wire that lies in the magnetic field is 0.060 m. When the switch is closed, a current of 4.0
A flows through the wire from point P to point Q.
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Physics 25 Examination 3 March 28, 2012 Dr. Alward
A)
B)
C)
D)
E)
4.Which one of the following statements concerning the effect of the magnetic force on the
wire is true?
The wire will be pushed to the left.
The wire will be pushed to the right.
The wire will have no net force acting on it.
The wire will be pushed downward, into the plane of the paper.
None of these
A)
B)
C)
D)
E)
5.What is the magnitude of the magnetic force acting on the wire?
0.12 N
0.24 N
0.48 N
67 N
None of these
6.The radius of a coil of wire with N turns is r = 0.28 m. A clockwise current of Icoil = 1.0 A
flows in the coil, as shown. A long, straight wire carrying a current Iwire = 29 A toward
the left is located 0.04 m from the edge of the coil. The magnetic field at the center of the
coil is zero tesla. Determine N, the number of turns.
A)
B)
C)
D)
E)
A)
B)
C)
D)
E)
8
2
6
4
None of these
7.A long, straight wire carries a current I. If the magnetic field at a distance d from the
wire has magnitude B, what is the magnitude of the magnetic field at a distance 2d from
the wire?
B/2
B/4
2B
4B
None of these
8.A coil of wire carries current I as shown in the figure. If the observer could “see” the
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Physics 25 Examination 3 March 28, 2012 Dr. Alward
magnetic field inside this arrangement of loops, how would it appear?
A)
B)
C)
D)
E)
a
b
c
d
None of these
9.Four long, straight wires are parallel to each other; and their cross-section forms a square.
Each side of the square is 0.020 m as shown in the figure. If each wire carries a current
of 8.0 A in the direction shown in the figure, determine the magnitude of the total
magnetic field at P, the center of the square.
A)
B)
C)
D)
E)
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5.1 × 10–5 T
1.1 × 10–4 T
1.7 × 10–4 T
2.3 × 10–4 T
None of these
Physics 25 Examination 3 March 28, 2012 Dr. Alward
Use the following to answer question 10:
Two long, straight, parallel wires separated by a distance d carry currents in opposite directions
as shown in the figure. The bottom wire carries a current of 6.0 A. Point C is at the midpoint
between the wires and point O is a distance 0.50d below the 6-A wire as suggested in the figure.
The total magnetic field at point O is zero tesla.
A)
B)
C)
D)
E)
10.Determine the magnitude of the magnetic field at point C if d = 0.10 m.
2.4 × 10–5 T
4.8 × 10–5 T
9.6 × 10–5 T
1.1 × 10–4 T
None of these
Use the following to answer question 11:
Two long, straight wires separated by 0.10 m carry currents of 18 A and 6 A in the same
direction as shown.
A)
B)
C)
D)
E)
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11.Determine the magnitude of the magnetic field at the point P.
2.4 × 10–5 T
4.8 × 10–5 T
7.2 × 10–5 T
9.6 × 10–5 T
None of these
Physics 25 Examination 3 March 28, 2012 Dr. Alward
12.A long, straight wire is in the same plane as a rectangular, conducting loop. The wire
carries a constant current I as shown in the figure. Which one of the following statements
is true if the wire is suddenly moved toward the loop?
A)
B)
C)
D)
E)
There will be no induced emf and no induced current.
There will be an induced emf, but no induced current.
There will be an induced current that is clockwise around the loop.
There will be an induced current that is counterclockwise around the loop.
None of these
13.A metal ring is dropped from rest below a bar magnet that is fixed in position as
suggested in the figure. An observer views the ring from below. Which one of the
following statements concerning this situation is true?
A)
B)
C)
D)
E)
As the ring falls, an induced current will flow counterclockwise as viewed by the
observer.
As the ring falls, an induced current will flow clockwise as viewed by the observer.
As the ring falls, there will be an induced magnetic field around the ring that appears
counterclockwise as viewed by the observer.
As the ring falls, there will be an induced magnetic field around the ring that appears
clockwise as viewed by the observer.
None of these
14.A woman stands 2.0 m in front of a convex mirror and notices that her image height is
1/4 of her actual height. Determine the radius of curvature of the mirror.
A)
0.67 m
B)
1.3 m
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Physics 25 Examination 3 March 28, 2012 Dr. Alward
C)
D)
E)
2.0 m
4.0 m
None of these
A)
B)
C)
D)
E)
15.What would the speed of an observer be if a red (4.688 × 1014 Hz) traffic light appeared
green (5.555 × 1014 Hz) to the observer?
4.445 × 108 m/s
2.219 × 108 m/s
8.438 × 107 m/s
5.548 × 107 m/s
None of these
A)
B)
C)
D)
E)
16.A spherical concave mirror has a radius of curvature of 6.0 cm. At what distance from
the mirror should a 6.0-cm object be placed to obtain an image that is 48 cm tall?
1.3 cm
3.6 cm
4.2 cm
5.3 cm
None of these
A)
B)
C)
D)
E)
17.A convex mirror has a radius of curvature of 0.50 m. Where must an object be placed in
front of the mirror such that the image is formed 0.15 m behind the mirror?
0.38 m
0.19 m
0.77 m
0.093 m
None of these
A)
B)
C)
D)
E)
18.An object is placed 20.0 cm in front of a convex spherical mirror with radius of curvature
60.0 cm. Which one of the following phrases best describes the image?
virtual and located at infinity
real and located 12 cm from the mirror
real and located 17 cm from the mirror
virtual and located 12 cm from the mirror
None of these
19.The inverted image of a light bulb is formed on a screen located 9.00 m from a spherical
mirror. The image is 4.00 times larger than the light bulb. Determine the object distance
and the type of mirror used.
A)
+0.444 m, concave
B)
+2.25 m, concave
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Physics 25 Examination 3 March 28, 2012 Dr. Alward
C)
D)
E)
+36.0 m. concave
+0.0278 m, convex
None of these
20.A 0.0150-m wire oriented horizontally between the poles of an electromagnet carries a
direct current of 9.5 A. The angle between the direction of the current and that of the
magnetic field is 25.0° as shown. If the magnetic field strength is 0.845 T, what is the
magnitude and direction of the magnetic force on the wire between the poles?
A)
B)
C)
D)
E)
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1.17 N, upward
0.330 N, downward
0.0509 N, upward
0.120 N, downward
None of these
Physics 25 Examination 3 March 28, 2012 Dr. Alward
Answer Key
1.A
2.C
3.D
4.D
5.C
6.A
7.A
8.C
9.D
10.C
11.B
12.D
13.A
14.B
15.D
16.B
17.A
18.D
19.B
20.C
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