Download Magnetism Problem Set #2

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AP PHYSICS 2
Magnetism Problem Set #2
1. The figure to the right shows a long conducting wire
that lies in the plane of the page and carries an electric
current I toward the right. At the instant shown, a
positive point charge +q is in the plane of the page and
moving toward the bottom of the page. What is the
direction of the magnetic force on the point charge at
that instant?
(A) Into the page
(B) Out of the page
(C) Toward the right
(D) Toward the left
Briefly explain your answer.
2. A scientist is studying the radioactive decay of an
element and wants to determine the sign of some
of the particles emitted. The scientist lets a beam
of the particles, all with the same speed, pass
through an opening in a shield and enter the field
created by a wire carrying a constant current.
Paths 1 and 2 represent the observed paths of the
particles. Based on the paths, which of the
following could be the charges of the particles?
Particle on
path 1
(A) - charge
(B) + charge
(C) + charge
(D) - charge
Briefly explain your answer.
Particle on
path 2
+ charge
- charge
+ charge
- charge
3. The figure above shows a long, straight wire that has a steady
current I in the +y-direction. A small object with charge +q
hangs from a thread near the wire. A student wants to
investigate the magnetic force on the object due to the current
but is not able to observe or measure changes in the tension in
the string. Of the following actions that the student can take,
which will allow the student to observe a reaction of the object
due to the magnetic force on it?
(A)
(B)
(C)
(D)
Holding the object motionless
Moving the object in a circle that is centered on the wire and in the x - z plane
Moving the object in the -x-direction
Moving the object in the +y-direction
Briefly explain your answer.
4. At the instant shown at the right, an electron is
moving to the right along a straight line midway
between two identical bar magnets. Which of
the following describes the path of the electron
as it continues to move?
(A) It remains on the straight line and
passes completely between the magnets.
(B) It curves upward and strikes the top magnet.
(C) It curves downward and reverses direction before it enters the space between the
magnets.
(D) It stops and reverses direction, then moves to the left along the same straight line.
Briefly explain your answer.
AP Physics 2
Magnetism 2 Problem Set
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5.
A beam of electrons travels between two parallel wire coils, as shown in the figures above.
When the coils carry no current, the electron beam is undeflected and hits the center of
the screen, as indicated by the dashed line. When a constant current I in the indicated
direction is created in the coils,
the electron beam is deflected
toward which edge of the
screen?
(A) The top
(B) The bottom
(C) The left
(D) None: it is not deflected
Briefly explain your answer.
Use the scenario below to answer questions 6-8.
The force on a wire is a maximum of 8.50 x 10-2 N when placed between the pole faces of two magnets.
The current flows horizontally to the right and the magnetic field is vertical. The wire is observed to
jump towards the observer when the current is turned on. (Giancoli, 20-7)
6. What polarity (north or south) is the part of the magnet closest to the wire of the upward-facing
magnet? Briefly explain your answer.
7. If the pole faces have a diameter of 10.0 cm and the field strength is 0.220 T, estimate the current of
the wire.
8. If the wire is tipped so that it makes an angle of 10.0 with the horizontal, what force will it now
feel? (Hint: what length of wire is now in the field?)
AP Physics 2
Magnetism 2 Problem Set
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9. Jumper cables used to start a stalled vehicle often carry a current of 65 A. How strong is the
magnetic field 4.5 cm from one cable? Compare to Earth’s magnetic field, 5.0 x 10-5 T. (Giancoli,
20-25)
Use the scenario below to answer questions 10-11.
A power line carries a current of 95 A west along the tops of 8.5-m-high poles. (Giancoli, 20-38)
10. What is the magnitude and direction of the magnetic field produced by this wire at the ground
directly below? How does this compare with the Earth’s magnetic field of 5.0 x 10-5 T?
11. Where would the wire’s magnetic field cancel the Earth’s field?
12. A thin, 12-cm long solenoid has a total of 460 turns of wire and carries a current of 2.0 A. Calculate
the field inside the solenoid near the center. (Giancoli, 20-44)
AP Physics 2
Magnetism 2 Problem Set
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13. A 30-cm long solenoid 1.25 cm in diameter is to produce a field of 4.65 mT at its center. How
much current should the solenoid carry if it has 935 turns of wire? (Giancoli, 20-45)
14. A 42-cm long solenoid, 1.8 cm in diameter, is to produce a 0.030-T magnetic field at its center. If
the maximum current is 4.5 A, how many turns must the solenoid have? (Giancoli, 20-46)
15. If you have 1.0 kg of copper and want to make a practical solenoid that produces the greatest
possible magnetic field for a given voltage. Would you make your copper wire long and thin, short
and fat, or something else? Consider other variables, such as solenoid diameter, length and so on.
Explain your reasoning. (Giancoli, 20-48) (Hint: revisit mathematical definition of resistivity.)
Use the scenario below to answer questions 16 – 20.
An electron is moving north at a constant speed of 3.0 x 104 m/s. (Giancoli, 20-S&L 2)
16. In what direction should an electric field point if the electron is to be accelerated to the east?
Briefly explain your answer.
AP Physics 2
Magnetism 2 Problem Set
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17. In what direction should a magnetic field point if the electron is to be accelerated to the west?
Briefly explain your answer.
18. If the electric field from question 16 has a field strength of 330 N/C, what magnetic field (magnitude
and direction) will produce a zero net force on the electron?
19. If the electron from question 18 is moving faster than 3.0 x 104 m/s, in which direction will it be
accelerated? What if it is moving slower than 3.0 x 104 m/s? Briefly explain your answer.
20. Now consider electrons that move perpendicular to both a magnetic field and to an electric field
which are perpendicular to each other. If only electrons with speeds of 5.5 x 104 m/s go straight
through undeflected, what is the ratio of the magnitudes of electric field to magnetic field?
AP Physics 2
Magnetism 2 Problem Set
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