Question 1

A straight bar magnet is initially 4 cm long, with the north pole on the right and the south pole on the left. If you cut the magnet in half, the right half will

Accepted Answer

A)  contain only a south pole. 
B)  contain only a north pole. 
C)  contain a north pole on the right and a south pole on the left. 
D)  no longer contain any poles. 
A)  contain only a south pole. 
B)  contain only a north pole. 
C)  contain a north pole on the right and a south pole on the left. 
D)  no longer contain any poles.

Question 2

How much current must flow through a long straight wire for the magnetic field strength to be $1.0$ $\mathrm { mT }$ at $1.0 \mathrm {~cm}$ from a wire? $\left( \mu _ { 0 } = 4 \pi \times 10 ^ { - 7 } \mathrm {~T} \cdot \mathrm { m } / \mathrm { A } \right)$

Accepted Answer

A)  $9.2 \mathrm {~A}$ 
B)  $5.0 \mathrm {~mA}$ 
C)  $50 \mathrm {~A}$ 
D)  $50 \mathrm {~mA}$ 
E)  $16 \mathrm {~A}$ 
A)  $9.2 \mathrm {~A}$ 
B)  $5.0 \mathrm {~mA}$ 
C)  $50 \mathrm {~A}$ 
D)  $50 \mathrm {~mA}$ 
E)  $16 \mathrm {~A}$

Question 3

A proton, moving in a uniform magnetic field, moves in a circle perpendicular to the field lines and takes time T for each circle. If the proton's speed tripled, what would now be its time to go around
Each circle?

Accepted Answer

A)  $T / 9$ 
B)  $3 T$ 
C)  $9 T$ 
D)  $T$ 
E)  $T / 3$ 
A)  $T / 9$ 
B)  $3 T$ 
C)  $9 T$ 
D)  $T$ 
E)  $T / 3$

Question 4

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

Accepted Answer

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

Question 5

When two long parallel wires carry unequal currents, the magnitude of the magnetic force that one wire exerts on the other is F. If the current in both wires is now doubled, what is the magnitude of
The new magnetic force on each wire?

Accepted Answer

A)  $8 \mathrm {~F}$ 
B)  $2 F$ 
C)  $16 \mathrm {~F}$ 
D)  $4 \mathrm {~F}$ 
E)  $F \sqrt { 2 }$ 
A)  $8 \mathrm {~F}$ 
B)  $2 F$ 
C)  $16 \mathrm {~F}$ 
D)  $4 \mathrm {~F}$ 
E)  $F \sqrt { 2 }$

Question 6

An electron is moving to the right, as shown in the figure. Suddenly it encounters uniform magnetic field pointing out of the page. Which one of the three paths shown will it follow in the field?

Accepted Answer

A)  path a 
B)  path $b$ 
C)  path c 
A)  path a 
B)  path $b$ 
C)  path c

Question 7

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

Question 8

A proton travels at a speed of $5.0 \times 10 ^ { 7 } \mathrm {~m} / \mathrm { s }$ through a $1.0 - \mathrm { T }$ magnetic field. What is the magnitude of the magnetic force on the proton if the angle between the proton's velocity and the magnetic field vector is $30 ^ { \circ } ? \left( e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$

Accepted Answer

A)  $2.0 \times 10 ^ { - 12 } \mathrm {~N}$ 
B)  $2.0 \times 10 ^ { - 14 } \mathrm {~N}$ 
C)  $4.0 \times 10 ^ { - 14 } \mathrm {~N}$ 
D)  $4.0 \times 10 ^ { - 12 } \mathrm {~N}$ 
A)  $2.0 \times 10 ^ { - 12 } \mathrm {~N}$ 
B)  $2.0 \times 10 ^ { - 14 } \mathrm {~N}$ 
C)  $4.0 \times 10 ^ { - 14 } \mathrm {~N}$ 
D)  $4.0 \times 10 ^ { - 12 } \mathrm {~N}$

Question 9

Which one of the following statements is correct?

Accepted Answer

A)  Earth's geographic north pole is the north pole of Earth's magnetic field. 
B)  Earth's geographic south pole is the south pole of Earth's magnetic field. 
C)  The north pole of a magnet points towards Earth's geographic south pole. 
D)  The north pole of a magnet points towards Earth's geographic north pole. 
E)  None of the above statements is correct. 
A)  Earth's geographic north pole is the north pole of Earth's magnetic field. 
B)  Earth's geographic south pole is the south pole of Earth's magnetic field. 
C)  The north pole of a magnet points towards Earth's geographic south pole. 
D)  The north pole of a magnet points towards Earth's geographic north pole. 
E)  None of the above statements is correct.

Question 10

A proton moving with a velocity of $4.0 \times 10 ^ { 4 } \mathrm {~m} / \mathrm { s }$ enters a magnetic field of $0.20 \mathrm {~T}$. If the angle between the velocity of the proton and the direction of the magnetic field is $60 ^ { \circ }$, what is the magnitude of the magnetic force on the proton? $\left( e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$

Accepted Answer

A)  $0.60 \times 10 ^ { - 15 } \mathrm {~N}$ 
B)  $2.2 \times 10 ^ { - 15 } \mathrm {~N}$ 
C)  $1.1 \times 10 ^ { - 15 } \mathrm {~N}$ 
D)  $3.3 \times 10 ^ { - 15 } \mathrm {~N}$ 
E)  $1.8 \times 10 ^ { - 15 } \mathrm {~N}$ 
A)  $0.60 \times 10 ^ { - 15 } \mathrm {~N}$ 
B)  $2.2 \times 10 ^ { - 15 } \mathrm {~N}$ 
C)  $1.1 \times 10 ^ { - 15 } \mathrm {~N}$ 
D)  $3.3 \times 10 ^ { - 15 } \mathrm {~N}$ 
E)  $1.8 \times 10 ^ { - 15 } \mathrm {~N}$

Question 11

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

Accepted Answer

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

Question 12

A particle carrying a charge of +e travels in a circular path of radius R in a uniform magnetic field. If instead the particle carried a charge of +2e, the radius of the circular path would have been

Accepted Answer

A)  $R / 2$. 
B)  $R / 4$. 
C)  $2 R$. 
D)  $4 R$. 
E)  $8 R$. 
A)  $R / 2$. 
B)  $R / 4$. 
C)  $2 R$. 
D)  $4 R$. 
E)  $8 R$.

Question 13

The magnetic field due to the current in a long, straight wire is $8.0 \mu T$ at a distance of $4.0 \mathrm {~cm}$ from the center of the wire. What is the current in the wire? $\left( \mu _ { 0 } = 4 \pi \times 10 ^ { - 7 } \mathrm {~T} \cdot \mathrm { m } / \mathrm { A } \right)$

Accepted Answer

A)  $0.20 \mathrm {~A}$ 
B)  $3.2 \mathrm {~A}$ 
C)  $1.6 \mathrm {~A}$ 
D)  $0.80 \mathrm {~A}$ 
E)  $0.40 \mathrm {~A}$ 
A)  $0.20 \mathrm {~A}$ 
B)  $3.2 \mathrm {~A}$ 
C)  $1.6 \mathrm {~A}$ 
D)  $0.80 \mathrm {~A}$ 
E)  $0.40 \mathrm {~A}$

Question 14

A charged particle of mass 0.0040 kg is subjected to a 4.0-T magnetic field which acts at a right angle to its motion. If the particle moves in a circle of radius 0.10 m at a speed of 2.0 m/s, what is
The magnitude of the charge on the particle?

Accepted Answer

A)  0.00040 C 
B)  2500 C 
C)  0.020 C 
D)  50 C 
A)  0.00040 C 
B)  2500 C 
C)  0.020 C 
D)  50 C

Question 15

In a mass spectrometer, a single-charged particle has a speed of $1.00 \times 10 ^ { 6 } \mathrm {~m} / \mathrm { s }$ and enters a uniform magnetic field of $0.200 \mathrm {~T}$ at a right angle to the field. The radius of the resulting circular orbit is $20.75 \mathrm {~cm}$. What is the mass of the particle? $\left( e = 1.60 \times 10 ^ { - 19 } \mathrm { C } \right)$

Accepted Answer

A)  $1.67 \times 10 ^ { - 27 } \mathrm {~kg}$ 
B)  $3.20 \times 10 ^ { - 27 } \mathrm {~kg}$ 
C)  $9.11 \times 10 ^ { - 31 } \mathrm {~kg}$ 
D)  $6.64 \times 10 ^ { - 27 } \mathrm {~kg}$ 
A)  $1.67 \times 10 ^ { - 27 } \mathrm {~kg}$ 
B)  $3.20 \times 10 ^ { - 27 } \mathrm {~kg}$ 
C)  $9.11 \times 10 ^ { - 31 } \mathrm {~kg}$ 
D)  $6.64 \times 10 ^ { - 27 } \mathrm {~kg}$

Question 16

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

Accepted Answer

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

Question 17

A flat rectangular loop of wire is placed between the poles of a magnet, as shown in the figure. It has dimensions $w = 0.60 \mathrm {~m}$ and $L = 1.0 \mathrm {~m}$, and carries a current $I = 2.0 \mathrm {~A}$ in the direction shown. The magnetic field due to the magnet is uniform and of magnitude $0.80 \mathrm {~T}$. The loop rotates in the magnetic field and at one point the plane of the loop is perpendicular 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)  $0.40 \mathrm {~N} \cdot \mathrm { m }$ 
B)  0.30 N . m 
C)  $0.83 \mathrm {~N} \cdot \mathrm { m }$ 
D)  $0.96 \mathrm {~N} \cdot \mathrm { m }$ 
E)  $0.00 \mathrm {~N} \cdot \mathrm { m }$ 
A)  $0.40 \mathrm {~N} \cdot \mathrm { m }$ 
B)  0.30 N . m 
C)  $0.83 \mathrm {~N} \cdot \mathrm { m }$ 
D)  $0.96 \mathrm {~N} \cdot \mathrm { m }$ 
E)  $0.00 \mathrm {~N} \cdot \mathrm { m }$

Question 18

In the figure, a rectangular current loop is carrying current $I _ { 1 } = 7.0 \mathrm {~A}$, in the direction indicated, near a long wire carrying a current $I _ { \mathbf { W } }$. The long wire is parallel to the sides of the rectangle. The rectangle loop has length $0.80 \mathrm {~m}$ and its sides are $0.10 \mathrm {~m}$ and $0.70 \mathrm {~m}$ from the wire. If the net force on the loop is to have magnitude $1.7 \times 10 ^ { - 6 } \mathrm {~N}$ and is to be directed towards the wire, what must be the magnitude and direction (from top to bottom or from bottom to top in the sketch) of the current $I _ { W }$ in the wire? $\left( \mu _ { 0 } = 4 \pi \times 10 ^ { - 7 } \mathrm {~T} \right.$. $\mathrm { m } / \mathrm { A } )$

Accepted Answer

0.18 A, fr

Question 19

In the figure, a small particle of charge $- 1.9 \times 10 ^ { - 6 } \mathrm { C }$ and mass $m = 3.1 \times 10 ^ { - 12 } \mathrm {~kg}$ has speed $v _ { 0 } = 8.1 \times 10 ^ { 3 } \mathrm {~m} / \mathrm { s }$ 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 $R = 5.0 \mathrm {~cm}$. Find the magnitude and direction of the magnetic field in the region.

Accepted Answer

0.26 T, in

Question 20

We observe that a moving charged particle experiences no magnetic force. From this we can definitely conclude that

Accepted Answer

A)  either no magnetic field exists or the particle is moving perpendicular to the field. 
B)  the particle must be moving parallel to the magnetic field. 
C)  no magnetic field exists in that region of space. 
D)  the particle is moving at right angles to the magnetic field. 
E)  either no magnetic field exists or the particle is moving parallel to the field. 
A)  either no magnetic field exists or the particle is moving perpendicular to the field. 
B)  the particle must be moving parallel to the magnetic field. 
C)  no magnetic field exists in that region of space. 
D)  the particle is moving at right angles to the magnetic field. 
E)  either no magnetic field exists or the particle is moving parallel to the field.

Exam 20: Magnetism

A straight bar magnet is initially 4 cm long, with the north pole on the right and the south pole on the left. If you cut the magnet in half, the right half will

A proton, moving in a uniform magnetic field, moves in a circle perpendicular to the field lines and takes time T for each circle. If the proton's speed tripled, what would now be its time to go around Each circle?

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

When two long parallel wires carry unequal currents, the magnitude of the magnetic force that one wire exerts on the other is F. If the current in both wires is now doubled, what is the magnitude of The new magnetic force on each wire?

An electron is moving to the right, as shown in the figure. Suddenly it encounters uniform magnetic field pointing out of the page. Which one of the three paths shown will it follow in the field?

An electron 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

Which one of the following statements is correct?

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

A particle carrying a charge of +e travels in a circular path of radius R in a uniform magnetic field. If instead the particle carried a charge of +2e, the radius of the circular path would have been

A charged particle of mass 0.0040 kg is subjected to a 4.0-T magnetic field which acts at a right angle to its motion. If the particle moves in a circle of radius 0.10 m at a speed of 2.0 m/s, what is The magnitude of the charge on the particle?

A very long straight current-carrying wire produces a magnetic field of 20mT20 \mathrm { mT }20mT at a distance ddd from the wire. To measure a field of 5mT5 \mathrm { mT }5mT due to this wire, you would have to go to a distance from the wire of

We observe that a moving charged particle experiences no magnetic force. From this we can definitely conclude that

Introduction, Measurement, Estimating

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