Question 1

The direction of the force on a current-carrying wire in a magnetic field is

Accepted Answer

A)  perpendicular only to the current. 
B)  perpendicular only to the magnetic field. 
C)  perpendicular to both the current and the magnetic field. 
D)  in the direction opposite to the current. 
E)  in same direction as the current. 
A)  perpendicular only to the current. 
B)  perpendicular only to the magnetic field. 
C)  perpendicular to both the current and the magnetic field. 
D)  in the direction opposite to the current. 
E)  in same direction as the current.

Question 2

A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure If there is a current I flowing through this coil in the direction shown, what is the direction of the force acting on section AB of this coil?

Accepted Answer

A)  perpendicular to and into the page 
B)  perpendicular to and out of the page 
C)  in the direction of the magnetic field 
D)  in the opposite direction of the magnetic field 
E)  The force is zero. 
A)  perpendicular to and into the page 
B)  perpendicular to and out of the page 
C)  in the direction of the magnetic field 
D)  in the opposite direction of the magnetic field 
E)  The force is zero.

Question 3

A very long straight current-carrying wire produces a magnetic field of 20 mT at a distance d from the wire. To measure a field of 5 mT due to this wire, you would have to go to a distance from the wire of

Accepted Answer

A)  16d. 
B)  8d. 
C)  4d. 
D)  2d. 
E)  d $\sqrt { 2 }$ 
A)  16d. 
B)  8d. 
C)  4d. 
D)  2d. 
E)  d $\sqrt { 2 }$

Question 4

A flat rectangular loop of wire is placed between the poles of a magnet, as shown in the figure. It has dimensions w = 0.60 m and L = 1.0 m, and carries a current I = 2.0 A in the direction shown. The magnetic field due to the magnet is uniform and of magnitude 0.80 T. The loop rotates in the magnetic field and at one point the plane of the loop is parallel to the field. At that instant, what is the magnitude of the torque acting on the wire due to the magnetic field?

Accepted Answer

A)  0.00 N ∙ m 
B)  0.40 N ∙ m 
C)  0.48 N ∙ m 
D)  0.83 N ∙ m 
E)  0.96 N ∙ m 
A)  0.00 N ∙ m 
B)  0.40 N ∙ m 
C)  0.48 N ∙ m 
D)  0.83 N ∙ m 
E)  0.96 N ∙ m

Question 5

Two long parallel wires carry currents of 20 A and 5.0 A in opposite directions. The wires are separated by 0.20 m. What is the strength of the magnetic field midway between the two wires? (μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

A)  1.0 × 10-5 T 
B)  2.0 × 10-5 T 
C)  3.0 × 10-5 T 
D)  4.0 × 10-5 T 
E)  5.0 × 10-5 T 
A)  1.0 × 10-5 T 
B)  2.0 × 10-5 T 
C)  3.0 × 10-5 T 
D)  4.0 × 10-5 T 
E)  5.0 × 10-5 T

Question 6

A proton, with mass 1.67 × 10-27 kg and charge +1.6 × 10-19 C, is sent with velocity $2.3\times 10^4 \mathrm {~m} / \mathrm { s }$ in the +x direction into a region where there is a uniform electric field of magnitude 780 $ {~V} / \mathrm { m }$ in the +y direction. What must be the magnitude and direction of the uniform magnetic field in the region if the proton is to pass through undeflected? Assume that the magnetic field has no x component and neglect gravitational effects.

Accepted Answer

Question 7

A proton is to orbit Earth at the equator using Earth's magnetic field to supply part of the necessary centripetal force. In what direction should the proton move?

Accepted Answer

A)  upward 
B)  northward 
C)  southward 
D)  eastward 
E)  westward 
A)  upward 
B)  northward 
C)  southward 
D)  eastward 
E)  westward

Question 8

A horizontal wire carries a current straight toward you. From your point of view, the magnetic field caused by this current

Accepted Answer

A)  points directly away from you. 
B)  points to the left. 
C)  circles the wire in a clockwise direction. 
D)  circles the wire in a counter-clockwise direction. 
A)  points directly away from you. 
B)  points to the left. 
C)  circles the wire in a clockwise direction. 
D)  circles the wire in a counter-clockwise direction.

Question 9

A rigid rectangular loop, measuring 0.30 m by 0.40 m, carries a current of 5.5 A, as shown in the figure. A uniform external magnetic field of magnitude 2.9 T in the -x direction is present. Segment CD is in the xz-plane and forms a 35° angle with the z-axis, as shown. What is the magnitude of the torque that the magnetic field exerts on the loop?

Accepted Answer

A)  1.1 N ∙ m 
B)  0.73 N ∙ m 
C)  1.3 N ∙ m 
D)  1.4 N ∙ m 
E)  1.6 N ∙ m 
A)  1.1 N ∙ m 
B)  0.73 N ∙ m 
C)  1.3 N ∙ m 
D)  1.4 N ∙ m 
E)  1.6 N ∙ m

Question 10

A proton has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. This magnetic field must have a component

Accepted Answer

A)  to the west. 
B)  to the east. 
C)  upward. 
D)  downward. 
E)  to the north. 
A)  to the west. 
B)  to the east. 
C)  upward. 
D)  downward. 
E)  to the north.

Question 11

A flat rectangular loop of wire carrying a 4.0-A current is placed in a uniform 0.60-T magnetic field. The magnitude of the torque acting on this loop when the plane of the loop makes a 30° angle with the field is measured to be 1.1 N ∙ m. What is the area of this loop?

Accepted Answer

A)  0.20 m2 
B)  0.40 m2 
C)  0.26 m2 
D)  0.80 m2 
E)  0.53 m2 
A)  0.20 m2 
B)  0.40 m2 
C)  0.26 m2 
D)  0.80 m2 
E)  0.53 m2

Question 12

An ideal solenoid that is 34.0 cm long is carrying a current of 2.00 A. If the magnitude of the magnetic field generated at the center of the solenoid is 9.00 mT, how many turns of wire does this solenoid contain? 
(μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

A)  860 
B)  1590 
C)  2320 
D)  3180 
E)  1220 
A)  860 
B)  1590 
C)  2320 
D)  3180 
E)  1220

Question 13

What is the force per meter on a straight wire carrying 5.0 A when it is placed in a magnetic field of 0.020 T so that the wire makes an angle of 27° with respect to the magnetic field lines.

Accepted Answer

A)  0.022 N/m 
B)  0.045 N/m 
C)  0.17 N/m 
D)  0.26 N/m 
A)  0.022 N/m 
B)  0.045 N/m 
C)  0.17 N/m 
D)  0.26 N/m

Question 14

An electron moving perpendicular to a uniform magnetic field of 3.2 × 10-2 T moves in a circle of radius 0.40 cm. How fast is this electron moving? 
(e = 1.60 × 10-19 C, melectron = 9.11 × 10-31kg)

Accepted Answer

A)  2.2 × 107 m/s 
B)  1.9 × 107 m/s 
C)  1.9 × 106 m/s 
D)  3.0 × 107 m/s 
E)  0.80 × 107 m/s 
A)  2.2 × 107 m/s 
B)  1.9 × 107 m/s 
C)  1.9 × 106 m/s 
D)  3.0 × 107 m/s 
E)  0.80 × 107 m/s

Question 15

A flat circular coil of wire having 200 turns and diameter 6.0 cm carries a current of 7.0 A. It is placed in a magnetic field of $0.60 \mathrm {~T}$ with the plane of the coil making an angle of 30° with the magnetic field. What is the magnitude of the magnetic torque on the coil?

Accepted Answer

A)  2.1 N ∙ m 
B)  1.2 N ∙ m 
C)  3.9 N ∙ m 
D)  5.4 N ∙ m 
E)  1.0 N ∙ m 
A)  2.1 N ∙ m 
B)  1.2 N ∙ m 
C)  3.9 N ∙ m 
D)  5.4 N ∙ m 
E)  1.0 N ∙ m

Question 16

A proton is projected with a velocity of 7.0 km/s into a magnetic field of 0.60 T perpendicular to the motion of the proton. What is the magnitude of the magnetic force that acts on the proton? (e = 1.60 × 10-19C)

Accepted Answer

A)  0 N 
B)  3.4 × 10-16 N 
C)  4.2 × 10-16 N 
D)  13 × 10-16 N 
E)  6.7 × 10-16 N 
A)  0 N 
B)  3.4 × 10-16 N 
C)  4.2 × 10-16 N 
D)  13 × 10-16 N 
E)  6.7 × 10-16 N

Question 17

A charged particle moving along the +x-axis enters a uniform magnetic field pointing along the +z-axis. A uniform electric field is also present. Due to the combined effect of both fields, the particle does not change its velocity. What is the direction of the electric field?

Accepted Answer

A)  along the -y-axis 
B)  along the +y-axis 
C)  along the -x-axis 
D)  along the +x-axis 
E)  along the -z-axis 
A)  along the -y-axis 
B)  along the +y-axis 
C)  along the -x-axis 
D)  along the +x-axis 
E)  along the -z-axis

Question 18

A charged particle moving along the +x-axis enters a uniform magnetic field pointing along the +z-axis. Because of an electric field along the +y-axis, the charge particle does not change velocity. What is the sign of this particle?

Accepted Answer

A)  positive 
B)  negative 
C)  The particle could be either positive or negative. 
D)  None of the above choices is correct. 
A)  positive 
B)  negative 
C)  The particle could be either positive or negative. 
D)  None of the above choices is correct.

Question 19

A long, straight, horizontal wire carries current toward the east. An electron moves toward the east alongside and just south of the wire. What is the direction of the magnetic force on the electron?

Accepted Answer

A)  toward the north 
B)  toward the south 
C)  upward 
D)  downward 
E)  toward the west 
A)  toward the north 
B)  toward the south 
C)  upward 
D)  downward 
E)  toward the west

Question 20

How many turns should a 10-cm long ideal solenoid have if it is to generate a 1.5-mT magnetic field when 1.0 A of current runs through it? 
(μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

A)  12 
B)  15 
C)  120 
D)  1200 
E)  3200 
A)  12 
B)  15 
C)  120 
D)  1200 
E)  3200

Exam 24: Magnetic Fields and Forces

The direction of the force on a current-carrying wire in a magnetic field is

A rectangular coil, with corners labeled ABCD, has length L and width w. It is placed between the poles of a magnet, as shown in the figure If there is a current I flowing through this coil in the direction shown, what is the direction of the force acting on section AB of this coil?

A very long straight current-carrying wire produces a magnetic field of 20 mT at a distance d from the wire. To measure a field of 5 mT due to this wire, you would have to go to a distance from the wire of

Two long parallel wires carry currents of 20 A and 5.0 A in opposite directions. The wires are separated by 0.20 m. What is the strength of the magnetic field midway between the two wires? (μ0 = 4π × 10-7 T ∙ m/A)

A proton is to orbit Earth at the equator using Earth's magnetic field to supply part of the necessary centripetal force. In what direction should the proton move?

A horizontal wire carries a current straight toward you. From your point of view, the magnetic field caused by this current

A proton has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. This magnetic field must have a component

A flat rectangular loop of wire carrying a 4.0-A current is placed in a uniform 0.60-T magnetic field. The magnitude of the torque acting on this loop when the plane of the loop makes a 30° angle with the field is measured to be 1.1 N ∙ m. What is the area of this loop?

An ideal solenoid that is 34.0 cm long is carrying a current of 2.00 A. If the magnitude of the magnetic field generated at the center of the solenoid is 9.00 mT, how many turns of wire does this solenoid contain? (μ0 = 4π × 10-7 T ∙ m/A)

What is the force per meter on a straight wire carrying 5.0 A when it is placed in a magnetic field of 0.020 T so that the wire makes an angle of 27° with respect to the magnetic field lines.

An electron moving perpendicular to a uniform magnetic field of 3.2 × 10-2 T moves in a circle of radius 0.40 cm. How fast is this electron moving? (e = 1.60 × 10-19 C, melectron = 9.11 × 10-31kg)

A flat circular coil of wire having 200 turns and diameter 6.0 cm carries a current of 7.0 A. It is placed in a magnetic field of 0.60 T0.60 \mathrm {~T}0.60 T with the plane of the coil making an angle of 30° with the magnetic field. What is the magnitude of the magnetic torque on the coil?

A proton is projected with a velocity of 7.0 km/s into a magnetic field of 0.60 T perpendicular to the motion of the proton. What is the magnitude of the magnetic force that acts on the proton? (e = 1.60 × 10-19C)

A charged particle moving along the +x-axis enters a uniform magnetic field pointing along the +z-axis. A uniform electric field is also present. Due to the combined effect of both fields, the particle does not change its velocity. What is the direction of the electric field?

A charged particle moving along the +x-axis enters a uniform magnetic field pointing along the +z-axis. Because of an electric field along the +y-axis, the charge particle does not change velocity. What is the sign of this particle?

A long, straight, horizontal wire carries current toward the east. An electron moves toward the east alongside and just south of the wire. What is the direction of the magnetic force on the electron?

How many turns should a 10-cm long ideal solenoid have if it is to generate a 1.5-mT magnetic field when 1.0 A of current runs through it? (μ0 = 4π × 10-7 T ∙ m/A)

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Two long parallel wires carry currents of 20 A and 5.0 A in opposite directions. The wires are separated by 0.20 m. What is the strength of the magnetic field midway between the two wires? (μ₀ = 4π × 10^-7 T ∙ m/A)

An ideal solenoid that is 34.0 cm long is carrying a current of 2.00 A. If the magnitude of the magnetic field generated at the center of the solenoid is 9.00 mT, how many turns of wire does this solenoid contain? (μ₀ = 4π × 10^-7 T ∙ m/A)

An electron moving perpendicular to a uniform magnetic field of 3.2 × 10^-2 T moves in a circle of radius 0.40 cm. How fast is this electron moving? (e = 1.60 × 10^-19 C, m_electron = 9.11 × 10^-31kg)

A flat circular coil of wire having 200 turns and diameter 6.0 cm carries a current of 7.0 A. It is placed in a magnetic field of $0.60 \mathrm {~T}$ with the plane of the coil making an angle of 30° with the magnetic field. What is the magnitude of the magnetic torque on the coil?

A proton is projected with a velocity of 7.0 km/s into a magnetic field of 0.60 T perpendicular to the motion of the proton. What is the magnitude of the magnetic force that acts on the proton? (e = 1.60 × 10^-19C)

How many turns should a 10-cm long ideal solenoid have if it is to generate a 1.5-mT magnetic field when 1.0 A of current runs through it? (μ₀ = 4π × 10^-7 T ∙ m/A)