Magnetic Fields Multiple-Choice Practice Questions | AP Physics C Electricity and Magnetism - Grade 9 PDF Download

 Page 1


Section I: Multiple Choice
1. Which of the following statements is/are true?
I. Magnetic force can never do work on a charged particle.
II. Magnetic force can never change the velocity of a charged particle.
III. A charged particle will always experience a magnetic force if it moves through a magnetic
field.
(A) I only
(B) I and II only
(C) II and III only
(D) III only
(E) None of the above
2. The velocity of a particle of charge +4.0 × 10
-9
 C and mass 2 × 10
-4
 kg is perpendicular to a
0.1-tesla magnetic field. If the particle’s speed is 3 × 10
4
 m/s, what is the acceleration of this
particle due to the magnetic force?
(A) 0.0006 m/s
2
(B) 0.006 m/s
2
(C) 0.06 m/s
2
(D) 0.6 m/s
2
(E) None of the above
3. In the figure below, what is the direction of the magnetic force F
B
 ?
(A) To the right
(B) Downward, in the plane of the page
(C) Upward, in the plane of the page
(D) Out of the plane of the page
(E) Into the plane of the page
4. In the figure below, what must be the direction of the particle’s velocity, v ?
Page 2


Section I: Multiple Choice
1. Which of the following statements is/are true?
I. Magnetic force can never do work on a charged particle.
II. Magnetic force can never change the velocity of a charged particle.
III. A charged particle will always experience a magnetic force if it moves through a magnetic
field.
(A) I only
(B) I and II only
(C) II and III only
(D) III only
(E) None of the above
2. The velocity of a particle of charge +4.0 × 10
-9
 C and mass 2 × 10
-4
 kg is perpendicular to a
0.1-tesla magnetic field. If the particle’s speed is 3 × 10
4
 m/s, what is the acceleration of this
particle due to the magnetic force?
(A) 0.0006 m/s
2
(B) 0.006 m/s
2
(C) 0.06 m/s
2
(D) 0.6 m/s
2
(E) None of the above
3. In the figure below, what is the direction of the magnetic force F
B
 ?
(A) To the right
(B) Downward, in the plane of the page
(C) Upward, in the plane of the page
(D) Out of the plane of the page
(E) Into the plane of the page
4. In the figure below, what must be the direction of the particle’s velocity, v ?
(A) To the right
(B) Downward, in the plane of the page
(C) Upward, in the plane of the page
(D) Out of the plane of the page
(E) Into the plane of the page
5. The picture above shows a positively charged particle, q, about to enter a rectangular area with
a magnetic field directed into the plane of the page. Assume that the particle WILL escape the
magnetic field. If it does so, it will exit
(A) somewhere along length A
(B) somewhere along length B
(C) at point C
(D) somewhere along length D
(E) somewhere along length E
6. A straight wire of length 2 m carries a 10-amp current. How strong is the magnetic field at a
distance of 2 cm from the wire?
(A) 1 × 10
-6
 T
(B) 1 × 10
-5
 T
Page 3


Section I: Multiple Choice
1. Which of the following statements is/are true?
I. Magnetic force can never do work on a charged particle.
II. Magnetic force can never change the velocity of a charged particle.
III. A charged particle will always experience a magnetic force if it moves through a magnetic
field.
(A) I only
(B) I and II only
(C) II and III only
(D) III only
(E) None of the above
2. The velocity of a particle of charge +4.0 × 10
-9
 C and mass 2 × 10
-4
 kg is perpendicular to a
0.1-tesla magnetic field. If the particle’s speed is 3 × 10
4
 m/s, what is the acceleration of this
particle due to the magnetic force?
(A) 0.0006 m/s
2
(B) 0.006 m/s
2
(C) 0.06 m/s
2
(D) 0.6 m/s
2
(E) None of the above
3. In the figure below, what is the direction of the magnetic force F
B
 ?
(A) To the right
(B) Downward, in the plane of the page
(C) Upward, in the plane of the page
(D) Out of the plane of the page
(E) Into the plane of the page
4. In the figure below, what must be the direction of the particle’s velocity, v ?
(A) To the right
(B) Downward, in the plane of the page
(C) Upward, in the plane of the page
(D) Out of the plane of the page
(E) Into the plane of the page
5. The picture above shows a positively charged particle, q, about to enter a rectangular area with
a magnetic field directed into the plane of the page. Assume that the particle WILL escape the
magnetic field. If it does so, it will exit
(A) somewhere along length A
(B) somewhere along length B
(C) at point C
(D) somewhere along length D
(E) somewhere along length E
6. A straight wire of length 2 m carries a 10-amp current. How strong is the magnetic field at a
distance of 2 cm from the wire?
(A) 1 × 10
-6
 T
(B) 1 × 10
-5
 T
(C) 2 × 10
-5
 T
(D) 1 × 10
-4
 T
(E) 2 × 10
-4
 T
7. Two long, straight wires are hanging parallel to each other and are 1 cm apart. The current in
Wire 1 is 5 A, and the current in Wire 2 is 10 A in the same direction. Which of the following
best describes the magnetic force per unit length felt by the wires?
(A) The force per unit length on Wire 1 is twice the force per unit length on Wire 2.
(B) The force per unit length on Wire 2 is twice the force per unit length on Wire 1.
(C) The force per unit length on Wire 1 is 0.0003 N/m, away from Wire 2.
(D) The force per unit length on Wire 1 is 0.001 N/m, toward Wire 2.
(E) The force per unit length on Wire 1 is 0.001 N/m, away from Wire 2.
8. In the figure above, two concentric rings have current running through them in the directions
shown. Assuming that both currents can be adjusted to any magnitude other than 0 (but
always in the directions shown), where is it possible for the net magnetic field to be 0 ?
I. Inside the inner ring
II. Between the two rings
III. Outside the outer ring
(A) I only
(B) I and III only
(C) II only
(D) II and III only
(E) None of the above
9. How many windings must a solenoid of length 80 cm have in order to establish a magnetic
field of strength 0.2 T inside the solenoid, if it carries a current of 20 amps?
(A)  1,000
(B)  6,400
(C) 10,000
Page 4


Section I: Multiple Choice
1. Which of the following statements is/are true?
I. Magnetic force can never do work on a charged particle.
II. Magnetic force can never change the velocity of a charged particle.
III. A charged particle will always experience a magnetic force if it moves through a magnetic
field.
(A) I only
(B) I and II only
(C) II and III only
(D) III only
(E) None of the above
2. The velocity of a particle of charge +4.0 × 10
-9
 C and mass 2 × 10
-4
 kg is perpendicular to a
0.1-tesla magnetic field. If the particle’s speed is 3 × 10
4
 m/s, what is the acceleration of this
particle due to the magnetic force?
(A) 0.0006 m/s
2
(B) 0.006 m/s
2
(C) 0.06 m/s
2
(D) 0.6 m/s
2
(E) None of the above
3. In the figure below, what is the direction of the magnetic force F
B
 ?
(A) To the right
(B) Downward, in the plane of the page
(C) Upward, in the plane of the page
(D) Out of the plane of the page
(E) Into the plane of the page
4. In the figure below, what must be the direction of the particle’s velocity, v ?
(A) To the right
(B) Downward, in the plane of the page
(C) Upward, in the plane of the page
(D) Out of the plane of the page
(E) Into the plane of the page
5. The picture above shows a positively charged particle, q, about to enter a rectangular area with
a magnetic field directed into the plane of the page. Assume that the particle WILL escape the
magnetic field. If it does so, it will exit
(A) somewhere along length A
(B) somewhere along length B
(C) at point C
(D) somewhere along length D
(E) somewhere along length E
6. A straight wire of length 2 m carries a 10-amp current. How strong is the magnetic field at a
distance of 2 cm from the wire?
(A) 1 × 10
-6
 T
(B) 1 × 10
-5
 T
(C) 2 × 10
-5
 T
(D) 1 × 10
-4
 T
(E) 2 × 10
-4
 T
7. Two long, straight wires are hanging parallel to each other and are 1 cm apart. The current in
Wire 1 is 5 A, and the current in Wire 2 is 10 A in the same direction. Which of the following
best describes the magnetic force per unit length felt by the wires?
(A) The force per unit length on Wire 1 is twice the force per unit length on Wire 2.
(B) The force per unit length on Wire 2 is twice the force per unit length on Wire 1.
(C) The force per unit length on Wire 1 is 0.0003 N/m, away from Wire 2.
(D) The force per unit length on Wire 1 is 0.001 N/m, toward Wire 2.
(E) The force per unit length on Wire 1 is 0.001 N/m, away from Wire 2.
8. In the figure above, two concentric rings have current running through them in the directions
shown. Assuming that both currents can be adjusted to any magnitude other than 0 (but
always in the directions shown), where is it possible for the net magnetic field to be 0 ?
I. Inside the inner ring
II. Between the two rings
III. Outside the outer ring
(A) I only
(B) I and III only
(C) II only
(D) II and III only
(E) None of the above
9. How many windings must a solenoid of length 80 cm have in order to establish a magnetic
field of strength 0.2 T inside the solenoid, if it carries a current of 20 amps?
(A)  1,000
(B)  6,400
(C) 10,000
(D) 32,000
(E) 64,000
10. The value of  • ds along a closed path in a magnetic field B is 6.28 × 10
-6
 T • m. What is the
total current that passes through this closed path?
(A) 0.1 A
(B) 0.5 A
(C) 1 A
(D) 4 A
(E) 5 A
Page 5


Section I: Multiple Choice
1. Which of the following statements is/are true?
I. Magnetic force can never do work on a charged particle.
II. Magnetic force can never change the velocity of a charged particle.
III. A charged particle will always experience a magnetic force if it moves through a magnetic
field.
(A) I only
(B) I and II only
(C) II and III only
(D) III only
(E) None of the above
2. The velocity of a particle of charge +4.0 × 10
-9
 C and mass 2 × 10
-4
 kg is perpendicular to a
0.1-tesla magnetic field. If the particle’s speed is 3 × 10
4
 m/s, what is the acceleration of this
particle due to the magnetic force?
(A) 0.0006 m/s
2
(B) 0.006 m/s
2
(C) 0.06 m/s
2
(D) 0.6 m/s
2
(E) None of the above
3. In the figure below, what is the direction of the magnetic force F
B
 ?
(A) To the right
(B) Downward, in the plane of the page
(C) Upward, in the plane of the page
(D) Out of the plane of the page
(E) Into the plane of the page
4. In the figure below, what must be the direction of the particle’s velocity, v ?
(A) To the right
(B) Downward, in the plane of the page
(C) Upward, in the plane of the page
(D) Out of the plane of the page
(E) Into the plane of the page
5. The picture above shows a positively charged particle, q, about to enter a rectangular area with
a magnetic field directed into the plane of the page. Assume that the particle WILL escape the
magnetic field. If it does so, it will exit
(A) somewhere along length A
(B) somewhere along length B
(C) at point C
(D) somewhere along length D
(E) somewhere along length E
6. A straight wire of length 2 m carries a 10-amp current. How strong is the magnetic field at a
distance of 2 cm from the wire?
(A) 1 × 10
-6
 T
(B) 1 × 10
-5
 T
(C) 2 × 10
-5
 T
(D) 1 × 10
-4
 T
(E) 2 × 10
-4
 T
7. Two long, straight wires are hanging parallel to each other and are 1 cm apart. The current in
Wire 1 is 5 A, and the current in Wire 2 is 10 A in the same direction. Which of the following
best describes the magnetic force per unit length felt by the wires?
(A) The force per unit length on Wire 1 is twice the force per unit length on Wire 2.
(B) The force per unit length on Wire 2 is twice the force per unit length on Wire 1.
(C) The force per unit length on Wire 1 is 0.0003 N/m, away from Wire 2.
(D) The force per unit length on Wire 1 is 0.001 N/m, toward Wire 2.
(E) The force per unit length on Wire 1 is 0.001 N/m, away from Wire 2.
8. In the figure above, two concentric rings have current running through them in the directions
shown. Assuming that both currents can be adjusted to any magnitude other than 0 (but
always in the directions shown), where is it possible for the net magnetic field to be 0 ?
I. Inside the inner ring
II. Between the two rings
III. Outside the outer ring
(A) I only
(B) I and III only
(C) II only
(D) II and III only
(E) None of the above
9. How many windings must a solenoid of length 80 cm have in order to establish a magnetic
field of strength 0.2 T inside the solenoid, if it carries a current of 20 amps?
(A)  1,000
(B)  6,400
(C) 10,000
(D) 32,000
(E) 64,000
10. The value of  • ds along a closed path in a magnetic field B is 6.28 × 10
-6
 T • m. What is the
total current that passes through this closed path?
(A) 0.1 A
(B) 0.5 A
(C) 1 A
(D) 4 A
(E) 5 A
Section I: Multiple Choice
1. A
Statement (I) is true because magnetic force always acts perpendicular to velocity,
meaning that the ? in W = Fd cos ? will always be 90°. Statement (II) is false because
magnetic force can change the direction of a moving charged particle (just not the speed).
Statement (III) is also false because the particle will feel no force if it moves parallel or
antiparallel to the magnetic field.
2. C
The magnitude of the magnetic force is F
B
 = qvB, so the acceleration of the particle has
magnitude
3. D
By the right-hand rule, the direction of v × B is into the plane of the page. Since the
particle carries a negative charge, the magnetic force it feels will be out of the page.
4. D
Since F
B
 is always perpendicular to v, v cannot be upward or downward in the plane of
the page; this eliminates (B) and (C). The velocity vector also cannot be to the right, since
then v would be antiparallel to B, and F
B
 would be zero, so (A) can be eliminated.
Because the charge is positive, the direction of F
B
 will be the same as the direction
of v× B. In order for v × B to be downward in the plane of the page, the right-hand rule
implies that v must be out of the plane of the page.
5. B
When a charged particle enters an external magnetic field, it will begin to move in a
circular motion. If the magnetic field is large enough, the particle will finish the circle and
remain in the field indefinitely. Using the right-hand rule, we can see that the particle in
question would immediately experience a force pushing toward the top of the page.
Continuing to apply the right-hand rule would make the particle move in a counter-
clockwise circle. However, if that result is being cut short, it would be because the
rectangle is not wide enough, meaning it could not complete its initial turn before exiting
the field somewhere along length B.
6. D
The strength of the magnetic field at a distance r from a long, straight wire carrying a
current I is given by the equation B = ( µ
0
/2p)( I/ r). Therefore,
7. D
By Newton’s Third Law, neither (A) nor (B) can be correct. Also, as we learned in Chapter
15, Example 9, if two parallel wires carry current in the same direction, the magnetic force
between them is attractive; this eliminates (C) and (E). Therefore, the answer must be