Question 1

In a velocity selector for ions, when the electric field is increased by 50%, what change in the magnetic field is necessary to select the same speed as before?

Accepted Answer

A)  a 50% decrease 
B)  a 25% decrease 
C)  no change 
D)  a 25% increase 
E)  a 50% increase 
A)  a 50% decrease 
B)  a 25% decrease 
C)  no change 
D)  a 25% increase 
E)  a 50% increase

Question 2

Two parallel wires are each carrying 10 A and are separated by 4.0 m. If the currents are in opposite directions, what is the magnitude of the magnetic field halfway between them?

Accepted Answer

A)  0.0 
B)  1.0 μT 
C)  2.0 μT 
D)  4.0 μT 
E)  1.4 μT 
A)  0.0 
B)  1.0 μT 
C)  2.0 μT 
D)  4.0 μT 
E)  1.4 μT

Question 3

Cathode rays are

Accepted Answer

A)  x-rays. 
B)  γ-rays. 
C)  electrons. 
D)  protons. 
E)  neutrons. 
A)  x-rays. 
B)  γ-rays. 
C)  electrons. 
D)  protons. 
E)  neutrons.

Question 4

Doubling the magnetic field in a proton cyclotron changes the maximum kinetic energy of the protons by what amount?

Accepted Answer

A)  It is quadrupled. 
B)  It is doubled. 
C)  It remains the same. 
D)  It is halved. 
E)  It is quartered. 
A)  It is quadrupled. 
B)  It is doubled. 
C)  It remains the same. 
D)  It is halved. 
E)  It is quartered.

Question 5

All materials fall into one of three magnetic categories. Select the category that is invalid.

Accepted Answer

A)  ferromagnetic 
B)  nonmagnetic 
C)  diamagnetic 
D)  paramagnetic 
A)  ferromagnetic 
B)  nonmagnetic 
C)  diamagnetic 
D)  paramagnetic

Question 6

A velocity selector for ions uses perpendicular electric and magnetic fields. If the electric field used were 800 V/m, what magnetic field would allow the selection of a velocity of 4000 m/s?

Accepted Answer

A)  0.0400 T 
B)  0.0800 T 
C)  0.160 T 
D)  0.200 T 
E)  0.500 T 
A)  0.0400 T 
B)  0.0800 T 
C)  0.160 T 
D)  0.200 T 
E)  0.500 T

Question 7

A wire bearing current of 1.25 A crosses a region in which there is a uniform B field of magnitude 1.0 T in the +y direction. The wire is inclined at an angle of 75 degrees above the +x direction, in the xy-plane. What is the magnitude of the force on the wire, if the magnetic field region spans 15 cm in the x direction?

Accepted Answer

A)  0.19 N 
B)  0.70 N 
C)  0.18 N 
D)  0.05 N 
A)  0.19 N 
B)  0.70 N 
C)  0.18 N 
D)  0.05 N

Question 8

A 3.0 cm section of a horizontal wire, carrying a 6.7 A current from east to west, is placed in a horizontal north-to-south 0.42 T uniform magnetic field in the lab. What is the magnitude of the force on the 3.0 cm section of the wire?

Accepted Answer

A)  0.084 N 
B)  0.17 N 
C)  0.25 N 
D)  0.0017 N 
E)  0.0025 N 
A)  0.084 N 
B)  0.17 N 
C)  0.25 N 
D)  0.0017 N 
E)  0.0025 N

Question 9

The magnetic field in a cyclotron is 0.50 T. What is the radius of the vacuum chamber for a maximum proton velocity of 1.0 × 107 m/s?

Accepted Answer

A)  0.11 m 
B)  1.2 m 
C)  0.21 m 
D)  0.013 m 
A)  0.11 m 
B)  1.2 m 
C)  0.21 m 
D)  0.013 m

Question 10

An electron is moving at 3.0 × 106 m/s perpendicular to a uniform magnetic field. If the radius of the motion is 18 mm, what is the magnitude of the magnetic field?

Accepted Answer

A)  70 mT 
B)  0.95 mT 
C)  9.3 mT 
D)  1.6 μT 
E)  8.9 nT 
A)  70 mT 
B)  0.95 mT 
C)  9.3 mT 
D)  1.6 μT 
E)  8.9 nT

Question 11

An electron is moving at 3.0 × 106 m/s at an angle of 40° to a 0.80 T magnetic field. What is the magnitude of the acceleration of the electron?

Accepted Answer

A)  2.7 × 1017 m/s2 
B)  1.4 × 1017 m/s2 
C)  5.2 × 1017 m/s2 
D)  7.8 × 1017 m/s2 
E)  9.8 × 1017 m/s2 
A)  2.7 × 1017 m/s2 
B)  1.4 × 1017 m/s2 
C)  5.2 × 1017 m/s2 
D)  7.8 × 1017 m/s2 
E)  9.8 × 1017 m/s2

Question 12

A coil of 150 turns of wire is in the form of a circle, carries a current of 63 mA, and sits in the center of a region of uniform magnetic field of strength 1.5 T. The torque on the coil has a maximum value of 0.25 N·m. What is the radius of the coils?

Accepted Answer

A)  9.2 cm 
B)  13 cm 
C)  0.56 cm 
D)  7.5 cm 
A)  9.2 cm 
B)  13 cm 
C)  0.56 cm 
D)  7.5 cm

Question 13

A solenoid of radius 1.1 cm, carrying a current of 2.2 A, produces a magnetic field at its center of 0.28 T. How many turns per unit length does the solenoid have?

Accepted Answer

A)  1.0 × 105 m−1 
B)  1.0 × 10−9 m−1 
C)  1.1 × 103 m−1 
D)  2.2 × 103 m−1 
E)  7.0 × 103 m−1 
A)  1.0 × 105 m−1 
B)  1.0 × 10−9 m−1 
C)  1.1 × 103 m−1 
D)  2.2 × 103 m−1 
E)  7.0 × 103 m−1

Question 14

An electron is moving at 2.5 × 106 m/s perpendicular to a uniform 3.5 mT magnetic field. What is the radius of its path?

Accepted Answer

A)  5.1 cm 
B)  3.9 cm 
C)  1.6 cm 
D)  4.1 mm 
E)  2.0 mm 
A)  5.1 cm 
B)  3.9 cm 
C)  1.6 cm 
D)  4.1 mm 
E)  2.0 mm

Question 15

If a charged particle is moving through a magnetic field with its velocity at an angle of 45 degrees with respect to the field, what happens to the magnetic force on it if both the speed and magnetic field are doubled?

Accepted Answer

A)  It stays the same. 
B)  It doubles. 
C)  It quadruples. 
D)  It halves. 
E)  It increases by a factor of 5.66. 
A)  It stays the same. 
B)  It doubles. 
C)  It quadruples. 
D)  It halves. 
E)  It increases by a factor of 5.66.

Question 16

In diagrams of magnetic fields, the symbol "×" is used to represent

Accepted Answer

A)  the region of no magnetic field. 
B)  the north magnetic field. 
C)  the magnetic field coming out of the paper. 
D)  the magnetic field going into the paper. 
E)  the magnetic field, regardless of direction. 
A)  the region of no magnetic field. 
B)  the north magnetic field. 
C)  the magnetic field coming out of the paper. 
D)  the magnetic field going into the paper. 
E)  the magnetic field, regardless of direction.

Question 17

A proton is moving perpendicular to a magnetic field at 3.0 × 106 m/s and experiences a magnetic force of magnitude 2.5 × 10−16 N. What is the magnitude of the magnetic field?

Accepted Answer

A)  0.52 T 
B)  3.8 × 10−2 T 
C)  1.9 × 10−3 T 
D)  2.6 × 10−4 T 
E)  5.2 × 10−4 T 
A)  0.52 T 
B)  3.8 × 10−2 T 
C)  1.9 × 10−3 T 
D)  2.6 × 10−4 T 
E)  5.2 × 10−4 T

Question 18

The temperature at which ferromagnetic materials transform into paramagnetic materials is called the

Accepted Answer

A)  Celsius temperature. 
B)  Carnot temperature. 
C)  Crossover temperature. 
D)  Curie temperature. 
E)  Chaos temperature. 
A)  Celsius temperature. 
B)  Carnot temperature. 
C)  Crossover temperature. 
D)  Curie temperature. 
E)  Chaos temperature.

Question 19

A charged particle of mass 1.0 × 10−26 kg enters a region of uniform magnetic field at a speed of 2.8 × 106 m/s, at an angle of 37 degrees relative to the magnetic field direction. If the magnetic field strength is 1.2 T and the charge of the particle is +e, what will be the radius of the helical path it takes?

Accepted Answer

A)  Insufficient information is given. 
B)  15 cm 
C)  11 cm 
D)  8.8 cm 
A)  Insufficient information is given. 
B)  15 cm 
C)  11 cm 
D)  8.8 cm

Question 20

The magnetic field inside a solenoid having 100 turns per cm and a current of 5.0 A is

Accepted Answer

A)  2.0 × 10−2 T. 
B)  1.0 × 10−2 T. 
C)  1.0 × 10−4 T. 
D)  6.3 × 10−4 T. 
E)  6.3 × 10−2 T. 
A)  2.0 × 10−2 T. 
B)  1.0 × 10−2 T. 
C)  1.0 × 10−4 T. 
D)  6.3 × 10−4 T. 
E)  6.3 × 10−2 T.

Exam 19: Magnetic Forces and Fields

In a velocity selector for ions, when the electric field is increased by 50%, what change in the magnetic field is necessary to select the same speed as before?

Two parallel wires are each carrying 10 A and are separated by 4.0 m. If the currents are in opposite directions, what is the magnitude of the magnetic field halfway between them?

Cathode rays are

Doubling the magnetic field in a proton cyclotron changes the maximum kinetic energy of the protons by what amount?

All materials fall into one of three magnetic categories. Select the category that is invalid.

A velocity selector for ions uses perpendicular electric and magnetic fields. If the electric field used were 800 V/m, what magnetic field would allow the selection of a velocity of 4000 m/s?

A 3.0 cm section of a horizontal wire, carrying a 6.7 A current from east to west, is placed in a horizontal north-to-south 0.42 T uniform magnetic field in the lab. What is the magnitude of the force on the 3.0 cm section of the wire?

The magnetic field in a cyclotron is 0.50 T. What is the radius of the vacuum chamber for a maximum proton velocity of 1.0 × 107 m/s?

An electron is moving at 3.0 × 106 m/s perpendicular to a uniform magnetic field. If the radius of the motion is 18 mm, what is the magnitude of the magnetic field?

An electron is moving at 3.0 × 106 m/s at an angle of 40° to a 0.80 T magnetic field. What is the magnitude of the acceleration of the electron?

A coil of 150 turns of wire is in the form of a circle, carries a current of 63 mA, and sits in the center of a region of uniform magnetic field of strength 1.5 T. The torque on the coil has a maximum value of 0.25 N·m. What is the radius of the coils?

A solenoid of radius 1.1 cm, carrying a current of 2.2 A, produces a magnetic field at its center of 0.28 T. How many turns per unit length does the solenoid have?

An electron is moving at 2.5 × 106 m/s perpendicular to a uniform 3.5 mT magnetic field. What is the radius of its path?

If a charged particle is moving through a magnetic field with its velocity at an angle of 45 degrees with respect to the field, what happens to the magnetic force on it if both the speed and magnetic field are doubled?

In diagrams of magnetic fields, the symbol "×" is used to represent

A proton is moving perpendicular to a magnetic field at 3.0 × 106 m/s and experiences a magnetic force of magnitude 2.5 × 10−16 N. What is the magnitude of the magnetic field?

The temperature at which ferromagnetic materials transform into paramagnetic materials is called the

The magnetic field inside a solenoid having 100 turns per cm and a current of 5.0 A is

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The magnetic field in a cyclotron is 0.50 T. What is the radius of the vacuum chamber for a maximum proton velocity of 1.0 × 10⁷ m/s?

An electron is moving at 3.0 × 10⁶ m/s perpendicular to a uniform magnetic field. If the radius of the motion is 18 mm, what is the magnitude of the magnetic field?

An electron is moving at 3.0 × 10⁶ m/s at an angle of 40° to a 0.80 T magnetic field. What is the magnitude of the acceleration of the electron?

An electron is moving at 2.5 × 10⁶ m/s perpendicular to a uniform 3.5 mT magnetic field. What is the radius of its path?

A proton is moving perpendicular to a magnetic field at 3.0 × 10⁶ m/s and experiences a magnetic force of magnitude 2.5 × 10⁻¹⁶ N. What is the magnitude of the magnetic field?