Question 1

A wire in the shape of an "M" lies in the plane of the paper. It carries a current of 2.0 A, flowing from A to E. It is placed in a uniform magnetic field of 0.85 T in the same plane, directed as shown on the right side of the figure. The figure indicates the dimensions of the wire. Note that AB is parallel to DE and to the baseline from which the magnetic field direction is measured. What are the magnitude and direction of the net force acting on this wire?

Accepted Answer

A)  0.40 N perpendicular out of the page 
B)  0.10 N perpendicular into the page 
C)  0.40 N perpendicular into the page 
D)  0.10 N perpendicular out of the page 
E)  0.20 N perpendicular out of the page

Question 2

A proton, moving west, enters a magnetic field. Because of this magnetic field the proton curves upward. We may conclude that the magnetic field must have a component

Accepted Answer

A)  towards the west. 
B)  towards the east. 
C)  towards the south. 
D)  towards the north. 
E)  downward.

Question 3

An electron moves with a speed of 8.0 × 106 m/s along the +x-axis. It enters a region where there is a magnetic field of 2.5 T, directed at an angle of 60° to the +x-axis and lying in the xy-plane. Calculate the magnitude of the magnetic force on the electron. (e = 1.60 × 10-19C)

Accepted Answer

A)  2.8 × 10-10 N 
B)  3.2 × 10-10 N 
C)  2.8 × 10-12 N 
D)  3.2 × 10-12 N 
E) 0N

Question 4

In the figure, the two long straight wires are separated by a distance of $d = 0.40 \mathrm {~m}$ The currents are $I_ 1$ = 1.0 A to the right in the upper wire and $I _ { 2 }$ = 8.0 A to the left in the lower wire. What are the magnitude and direction of the magnetic field at point P, that is a distance $d / 2 = 0.20 \mathrm {~m}$ below the lower wire? (μ₀ = 4π × 10^-7 T ∙ m/A)

Accepted Answer

The answer of In the figure, the two long straight...

Question 5

A proton, starting from rest, accelerates through a potential difference of 1.0 kV and then moves into a magnetic field of 0.040 T at a right angle to the field. What is the radius of the proton's resulting orbit? (e = 1.60 × 10-19 C, mproton = 1.67 × 10-27 kg)

Accepted Answer

A)  0.080 m 
B)  0.11 m 
C)  0.14 m 
D)  0.17 m

Question 6

In the figure, a small particle of charge -1.9 x $10^{ - 6}$ C and mass $m = 3.1 \times 10 ^ { - 12 } \mathrm {~kg}$ has speed $0 ^ { \prime } 0 = 8.1 \times 10 ^ { 3 } \mathrm {~m} / \mathrm { s }$ as it enters a region of uniform magnetic field. The particle is initially traveling perpendicular to the magnetic field and is observed to travel in the semicircular path shown with radius R = 5.0 cm. Find the magnitude and direction of the magnetic field in the region.

Accepted Answer

The answer of In the figure, a small particle of...

Question 7

An electron, moving west, enters a magnetic field. Because of this field the electron curves upward. We may conclude that the magnetic field must have a component

Accepted Answer

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

Question 8

A wire in the shape of an "M" lies in the plane of the paper. It carries a current of 2.0 A, flowing from A to E, as shown in the figure. It is placed in a uniform magnetic field of 0.55 T in the same plane, directed as shown on the right side of the figure. The figure indicates the dimensions of the wire. Note that AB is parallel to DE and to the baseline from which the magnetic field direction is measured. What are the magnitude and direction of the force acting on section CD of this wire?

Accepted Answer

A)  0.066 N perpendicular into the page 
B)  0.40 N perpendicular out of the page 
C)  0.066 N perpendicular out of the page 
D)  0.40 N perpendicular into the page 
E)  0.20 N perpendicular out of the page

Question 9

When you double the number of windings in an ideal solenoid while keeping all other parameters (radius, length and current) fixed, the magnetic field at the center of the solenoid will

Accepted Answer

A)  double. 
B)  triple. 
C)  quadruple. 
D)  be reduced by a factor of one-half. 
E)  be reduced by a factor of one-fourth.

Question 10

The magnetic force on a current-carrying wire in a magnetic field is the strongest when

Accepted Answer

A)  the current is in the direction of the magnetic field lines. 
B)  the current is in the direction opposite to the magnetic field lines. 
C)  the current is at a 180° angle with respect to the magnetic field lines. 
D)  the current is perpendicular to the magnetic field lines. 
E)  the current is at a 0° angle with respect to the magnetic field lines.

Question 11

Two long parallel wires are 0.400 m apart and carry currents of 4.00 A and 6.00 A. What is the magnitude of the force per unit length that each wire exerts on the other wire? (μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

A)  2.00 μN/m 
B)  5.00 μN/m 
C)  12.0 μN/m 
D)  16.0 μN/m 
E)  38.0 μN/m

Question 12

A wire in the shape of an "M" lies in the plane of the paper. It carries a current of 2.0 A, flowing from A to E, as shown in the figure. It is placed in a uniform magnetic field of 0.65 T in the same plane, directed as shown on the right side of the figure. The figure indicates the dimensions of the wire. Note that AB is parallel to DE and to the baseline from which the magnetic field direction is measured. What are the magnitude and direction of the force acting on section BC of this wire?

Accepted Answer

A)  0 N 
B)  0.090 N perpendicular out of the page 
C)  0.090 N perpendicular into the page 
D)  0.060 N perpendicular out of the page 
E)  none of the above

Question 13

Two long, parallel wires carry currents of different magnitudes. If the amount of current in one of the wires is doubled, what happens to the magnitude of the force that each wire exerts on the other?

Accepted Answer

A)  It is increased by a factor of 8. 
B)  It is increased by a factor of 4. 
C)  It is increased by a factor of 3. 
D)  It is increased by a factor of 2. 
E)  It is increased by a factor of $\sqrt { 2 }$

Question 14

A current-carrying loop of wire lies flat on a horizontal tabletop. When viewed from above, the current moves around the loop in a counterclockwise sense. For points on the tabletop outside the loop, the magnetic field lines caused by this current

Accepted Answer

A)  circle the loop in a clockwise direction. 
B)  circle the loop in a counterclockwise direction. 
C)  point straight up. 
D)  point straight down.

Question 15

If you were to cut a small permanent bar magnet in half,

Accepted Answer

A)  one piece would be a magnetic north pole and the other piece would be a south pole. 
B)  neither piece would be magnetic. 
C)  each piece would in itself be a smaller bar magnet with both north and south poles. 
D)  None of these statements is true.

Question 16

For the horseshoe magnet shown in the figure, the left end is a north magnetic pole and the right end is a south magnetic pole. When the switch is closed in the circuit, which way will the wire between the poles of the horseshoe magnet initially deflect?

Accepted Answer

A)  to the right 
B)  to the left 
C)  upward 
D)  downward

Question 17

Three long parallel wires each carry 2.0-A currents in the same direction. The wires are oriented vertically, and they pass through three of the corners of a horizontal square of side 4.0 cm. What is the magnitude of the magnetic field at the fourth (unoccupied) corner of the square due to these wires? 
(μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

A)  1.2 µT 
B)  2.1 µT 
C)  12 µT 
D)  21 µT 
E)  0 T

Question 18

A flat circular loop carrying a current of 2.0 A is in a magnetic field of 3.5 T. The loop has an area of 0.12 m2 and its plane is oriented at a 37° angle to the field. What is the magnitude of the magnetic torque on the loop?

Accepted Answer

A)  0.10 N ∙ m 
B)  0.51 N ∙ m 
C)  0.67 N ∙ m 
D)  46 N ∙ m

Question 19

An ideal solenoid 20 cm long is wound with 5000 turns of very thin wire. What strength magnetic field is produced at the center of the solenoid when a current of 10 A flows through it? (μ0 = 4π × 10-7 T ∙ m/A)

Accepted Answer

A)  0.0063 T 
B)  0.20 T 
C)  3.2 T 
D)  4.8 T 
E)  0.31 T

Question 20

An electron moving in the +y direction, at right angles to a magnetic field, experiences a magnetic force in the -x direction. The direction of the magnetic field is in the

Accepted Answer

A)  -x direction. 
B)  +x direction. 
C)  +y direction. 
D)  -z direction. 
E)  +z direction.

Exam 24: Magnetic Fields and Forces

A proton, moving west, enters a magnetic field. Because of this magnetic field the proton curves upward. We may conclude that the magnetic field must have a component

An electron moves with a speed of 8.0 × 10⁶ m/s along the +x-axis. It enters a region where there is a magnetic field of 2.5 T, directed at an angle of 60° to the +x-axis and lying in the xy-plane. Calculate the magnitude of the magnetic force on the electron. (e = 1.60 × 10^-19C)

A proton, starting from rest, accelerates through a potential difference of 1.0 kV and then moves into a magnetic field of 0.040 T at a right angle to the field. What is the radius of the proton's resulting orbit? (e = 1.60 × 10^-19 C, m_proton = 1.67 × 10^-27 kg)