Question 1

What is the radius of curvature of the path of a 3.0-keV proton in a perpendicular magnetic field of magnitude 0.80 T?

Accepted Answer

A) 9.9 mm 
B) 1.1 cm 
C) 1.3 cm 
D) 1.4 cm 
E) 7.6 mm 
A) 9.9 mm 
B) 1.1 cm 
C) 1.3 cm 
D) 1.4 cm 
E) 7.6 mm

Question 2

A charged particle (mass = m, charge = q > 0) moves in a region of space where the magnetic field has a constant magnitude of B and a downward direction. What is the magnetic force on the particle at an instant when it is moving horizontally toward the north with speed v?

Accepted Answer

A) qvB toward the east 
B) Zero 
C) qvB toward the west 
D) qvB upward 
E) qvB toward the south 
A) qvB toward the east 
B) Zero 
C) qvB toward the west 
D) qvB upward 
E) qvB toward the south

Question 3

A straight wire carries a current of 40 A in a uniform magnetic field (magnitude = 80 mT). If the force per unit length on this wire is 2.0 N/m, determine the angle between the wire and the magnetic field.

Accepted Answer

A) either 39° or 141° 
B) either 25° or 155° 
C) either 70° or 110° 
D) either 42° or 138° 
E) either 65° or 115° 
A) either 39° or 141° 
B) either 25° or 155° 
C) either 70° or 110° 
D) either 42° or 138° 
E) either 65° or 115°

Question 4

The diagram below shows the position of a long straight wire perpendicular to the page and a set of directions labeled A through H. When the current in the wire is directed up out of the page, the direction of the magnetic field at point P is

Accepted Answer

A) D. 
B) E. 
C) F. 
D) G. 
E) H. 
A) D. 
B) E. 
C) F. 
D) G. 
E) H.

Question 5

A rectangular coil (0.20 m × 0.80 m) has 200 turns and is in a uniform magnetic field of 0.30 T. When the orientation of the coil is varied through all possible positions, the maximum torque on the coil by magnetic forces is 0.080 N ⋅ m. What is the current in the coil?

Accepted Answer

A) 5.0 mA 
B) 1.7 A 
C) 8.3 mA 
D) 1.0 A 
E) 42 mA 
A) 5.0 mA 
B) 1.7 A 
C) 8.3 mA 
D) 1.0 A 
E) 42 mA

Question 6

A current of 4.0 A is maintained in a single circular loop having a circumference of 80 cm. An external magnetic field of 2.0 T is directed so that the angle between the field and the plane of the loop is 20°. Determine the magnitude of the torque exerted on the loop by the magnetic forces acting upon it.

Accepted Answer

A) 0.41 N ⋅ m 
B) 0.14 N ⋅ m 
C) 0.38 N ⋅ m 
D) 0.27 N ⋅ m 
E) 0.77 N ⋅ m 
A) 0.41 N ⋅ m 
B) 0.14 N ⋅ m 
C) 0.38 N ⋅ m 
D) 0.27 N ⋅ m 
E) 0.77 N ⋅ m

Question 7

On the average, in a ferromagnetic domain permanent atomic magnetic moments are aligned ____ to one another.

Accepted Answer

A) antiparallel 
B) parallel 
C) perpendicular 
D) alternately parallel and antiparallel 
E) randomly relative 
A) antiparallel 
B) parallel 
C) perpendicular 
D) alternately parallel and antiparallel 
E) randomly relative

Question 8

A proton is accelerated from rest through a potential difference of 2.5 kV and then moves perpendicularly through a uniform 0.60-T magnetic field. What is the radius of the resulting path?

Accepted Answer

A) 15 mm 
B) 12 mm 
C) 18 mm 
D) 24 mm 
E) 8.5 mm 
A) 15 mm 
B) 12 mm 
C) 18 mm 
D) 24 mm 
E) 8.5 mm

Question 9

An unusual lightning strike has a vertical portion with a positive current of +400 A upwards. The Earth's magnetic field at that location is parallel to the ground and has a magnitude of 30 μT. In N, the force exerted by the Earth's magnetic field on the 25-m-long current is

Accepted Answer

A) 0. 
B) 0.012 N, East. 
C) 0.012 N, West. 
D) 0.30 N, West. 
E) 300 N, East. 
A) 0. 
B) 0.012 N, East. 
C) 0.012 N, West. 
D) 0.30 N, West. 
E) 300 N, East.

Question 10

A proton with a kinetic energy of 0.20 keV follows a circular path in a region where the magnetic field is uniform and has a magnitude of 60 mT. What is the radius of this path?

Accepted Answer

A) 4.1 cm 
B) 2.9 cm 
C) 3.4 cm 
D) 5.1 cm 
E) 2.4 cm 
A) 4.1 cm 
B) 2.9 cm 
C) 3.4 cm 
D) 5.1 cm 
E) 2.4 cm

Question 11

A straight 10-cm wire bent at its midpoint so as to form an angle of 90° carries a current of 10 A. It lies in the xy plane in a region where the magnetic field is in the positive z direction and has a constant magnitude of 3.0 mT. What is the magnitude of the magnetic force on this wire?

Accepted Answer

A) 3.2 mN 
B) 2.1 mN 
C) 5.3 mN 
D) 4.2 mN 
E) 6.0 mN 
A) 3.2 mN 
B) 2.1 mN 
C) 5.3 mN 
D) 4.2 mN 
E) 6.0 mN

Question 12

The diagram below shows the position of a long straight wire perpendicular to the page and a set of directions labeled A through H.   When the current in the wire is directed up out of the page, the direction of the magnetic field at point P is

Accepted Answer

A) A. 
B) B. 
C) C. 
D) D. 
E) E. 
A) A. 
B) B. 
C) C. 
D) D. 
E) E.

Question 13

A straight wire is bent into the shape shown. Determine the net magnetic force on the wire when the current I travels in the direction shown in the magnetic field   . ​   ​

Accepted Answer

A) 2IBL in the −z direction 
B) 2IBL in the +z direction 
C) 4IBL in the +z direction 
D) 4IBL in the −z direction 
E) zero 
A) 2IBL in the −z direction 
B) 2IBL in the +z direction 
C) 4IBL in the +z direction 
D) 4IBL in the −z direction 
E) zero

Question 14

The diagram below shows the position of a long straight wire perpendicular to the page and a set of directions labeled A through H. When the current in the wire is directed up out of the page, the direction of the magnetic field at point P is

Accepted Answer

A) E. 
B) F. 
C) G. 
D) H. 
E) A. 
A) E. 
B) F. 
C) G. 
D) H. 
E) A.

Question 15

One reason why we know that magnetic fields are not the same as electric fields is because the force exerted on a charge +q

Accepted Answer

A) is in opposite directions in electric and magnetic fields. 
B) is in the same direction in electric and magnetic fields. 
C) is parallel to a magnetic field and perpendicular to an electric field. 
D) is parallel to an electric field and perpendicular to a magnetic field. 
E) is zero in both if the charge is not moving. 
A) is in opposite directions in electric and magnetic fields. 
B) is in the same direction in electric and magnetic fields. 
C) is parallel to a magnetic field and perpendicular to an electric field. 
D) is parallel to an electric field and perpendicular to a magnetic field. 
E) is zero in both if the charge is not moving.

Question 16

When a ferromagnetic material that has been magnetized is brought to a temperature greater than the Curie temperature, what happens to its residual magnetism?

Accepted Answer

A) Nothing happens to the residual magnetism. 
B) The residual magnetism disappears. 
C) The residual magnetism reaches it's highest value. 
D) All the magnetic domains causing magnetism become a single domain. 
E) The material of the magnet melts causing currents that are magnetic. 
A) Nothing happens to the residual magnetism. 
B) The residual magnetism disappears. 
C) The residual magnetism reaches it's highest value. 
D) All the magnetic domains causing magnetism become a single domain. 
E) The material of the magnet melts causing currents that are magnetic.

Question 17

An electron moving in the positive x direction experiences a magnetic force in the positive z direction. If Bx = 0, what is the direction of the magnetic field?

Accepted Answer

A) negative y direction 
B) positive y direction 
C) negative z direction 
D) positive z direction 
E) negative x direction 
A) negative y direction 
B) positive y direction 
C) negative z direction 
D) positive z direction 
E) negative x direction

Question 18

A proton is accelerated from rest through a potential difference of 150 V. It then enters a region of uniform magnetic field and moves in a circular path (radius = 12 cm). What is the magnitude of the magnetic field in this region?

Accepted Answer

A) 18 mT 
B) 12 mT 
C) 15 mT 
D) 22 mT 
E) 10 mT 
A) 18 mT 
B) 12 mT 
C) 15 mT 
D) 22 mT 
E) 10 mT

Question 19

An explorer walks into a lab in a science building. She has a compass in her hand and finds that the south pole of her compass points toward the room's east wall when she is nearer that wall and toward the west wall when she is nearer that wall. You could explain this if magnetized metal had been installed in the east and west walls with north poles pointing into the room. If no magnetic material was installed in the north or south walls of the room, she would expect that

Accepted Answer

A) the south pole of the compass would tend to point toward those walls. 
B) the north pole of the compass would tend to point toward those walls. 
C) the compass needle would not point in any particular direction. 
D) the north pole of the compass needle would tend to point toward the centers of those walls, but the south pole would tend to point toward the sides of those walls. 
E) the south pole of the compass needle would tend to point toward the centers of those walls, but the north pole would tend to point toward the sides of those walls. 
A) the south pole of the compass would tend to point toward those walls. 
B) the north pole of the compass would tend to point toward those walls. 
C) the compass needle would not point in any particular direction. 
D) the north pole of the compass needle would tend to point toward the centers of those walls, but the south pole would tend to point toward the sides of those walls. 
E) the south pole of the compass needle would tend to point toward the centers of those walls, but the north pole would tend to point toward the sides of those walls.

Question 20

You stand near the Earth's equator. A positively charged particle that starts moving parallel to the surface of the Earth in a straight line directed east is initially deflected upwards. If you know there are no electric fields in the vicinity, a possible reason why the particle does not initially acquire a downward component of velocity is because near the equator the magnetic field lines of the Earth are directed

Accepted Answer

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

Exam 30: Magnetic Fields and Forces

What is the radius of curvature of the path of a 3.0-keV proton in a perpendicular magnetic field of magnitude 0.80 T?

A charged particle (mass = m, charge = q > 0) moves in a region of space where the magnetic field has a constant magnitude of B and a downward direction. What is the magnetic force on the particle at an instant when it is moving horizontally toward the north with speed v?

A straight wire carries a current of 40 A in a uniform magnetic field (magnitude = 80 mT). If the force per unit length on this wire is 2.0 N/m, determine the angle between the wire and the magnetic field.

The diagram below shows the position of a long straight wire perpendicular to the page and a set of directions labeled A through H. When the current in the wire is directed up out of the page, the direction of the magnetic field at point P is

A rectangular coil (0.20 m × 0.80 m) has 200 turns and is in a uniform magnetic field of 0.30 T. When the orientation of the coil is varied through all possible positions, the maximum torque on the coil by magnetic forces is 0.080 N ⋅ m. What is the current in the coil?

On the average, in a ferromagnetic domain permanent atomic magnetic moments are aligned ____ to one another.

A proton is accelerated from rest through a potential difference of 2.5 kV and then moves perpendicularly through a uniform 0.60-T magnetic field. What is the radius of the resulting path?

An unusual lightning strike has a vertical portion with a positive current of +400 A upwards. The Earth's magnetic field at that location is parallel to the ground and has a magnitude of 30 μT. In N, the force exerted by the Earth's magnetic field on the 25-m-long current is

A proton with a kinetic energy of 0.20 keV follows a circular path in a region where the magnetic field is uniform and has a magnitude of 60 mT. What is the radius of this path?

A straight 10-cm wire bent at its midpoint so as to form an angle of 90° carries a current of 10 A. It lies in the xy plane in a region where the magnetic field is in the positive z direction and has a constant magnitude of 3.0 mT. What is the magnitude of the magnetic force on this wire?

The diagram below shows the position of a long straight wire perpendicular to the page and a set of directions labeled A through H. When the current in the wire is directed up out of the page, the direction of the magnetic field at point P is

A straight wire is bent into the shape shown. Determine the net magnetic force on the wire when the current I travels in the direction shown in the magnetic field . ​ ​

The diagram below shows the position of a long straight wire perpendicular to the page and a set of directions labeled A through H. When the current in the wire is directed up out of the page, the direction of the magnetic field at point P is

One reason why we know that magnetic fields are not the same as electric fields is because the force exerted on a charge +q

When a ferromagnetic material that has been magnetized is brought to a temperature greater than the Curie temperature, what happens to its residual magnetism?

An electron moving in the positive x direction experiences a magnetic force in the positive z direction. If Bx = 0, what is the direction of the magnetic field?

A proton is accelerated from rest through a potential difference of 150 V. It then enters a region of uniform magnetic field and moves in a circular path (radius = 12 cm). What is the magnitude of the magnetic field in this region?

Getting Started

One-Dimensional Motion

Vectors

Two- and Three-Dimensional Motion

Newtons Laws of Motion

Applications of Newtons Laws of Motion

Gravity

Conservation of Energy

Energy in Nonisolated Systems

Systems of Particles and Conservation of Momentum

Collisions

Rotation I: Kinematics and Dynamics

Rotation II: a Conservation Approach

Static Equilibrium, Elasticity, and Fracture

Fluids

Oscillations

Traveling Waves

Superposition and Standing Waves

Temperature, Thermal Expansion, and Gas Laws

Kinetic Theory of Gases

Heat and the First Law of Thermodynamics

Entropy and the Second Law of Thermodynamics

Electric Forces

Electric Fields

Gausss Law

Electric Potential

Capacitors and Batteries

Current and Resistance

Direct Current Dc Circuits

Gausss Law for Magnetism and Amperes Law

Faradays Law of Induction

Inductors and Ac Circuits

Maxwells Equations and Electromagnetic Waves

Diffraction and Interference

Applications of the Wave Model

Reflection and Images Formed by Reflection

Refraction and Images Formed by Refraction

Relativity

Filters

A straight wire is bent into the shape shown. Determine the net magnetic force on the wire when the current I travels in the direction shown in the magnetic field .