Question 1

In the formula

Accepted Answer

A)    must be perpendicular to   but not necessarily to   
B)    must be perpendicular to   but not necessarily to   
C)    must be perpendicular to   but not necessarily to   
D)  all three vectors must be mutually perpendicular 
E)    must be perpendicular to both   
A)    must be perpendicular to   but not necessarily to   
B)    must be perpendicular to   but not necessarily to   
C)    must be perpendicular to   but not necessarily to   
D)  all three vectors must be mutually perpendicular 
E)    must be perpendicular to both   E

Question 2

A loop of current-carrying wire has a magnetic dipole moment of 5 *10-4 A .m2. The moment initially is aligned with a 0.5-T magnetic filed.To rotate the loop so its dipole momentt is perpendicular to the field and hold it in that orentation, you must do work of:

Accepted Answer

A)  0 
B)  2.5 * 10-4 J 
C)  -2.5 * 10-4 J 
D)  1.0 * 10-3 J 
E)  -1.0 * 10-3 J 
A)  0 
B)  2.5 * 10-4 J 
C)  -2.5 * 10-4 J 
D)  1.0 * 10-3 J 
E)  -1.0 * 10-3 J B

Question 3

At any point the magnetic field lines are in the direction of:

Accepted Answer

A)  the magnetic force on a moving positive charge 
B)  the magnetic force on a moving negative charge 
C)  the velocity of a moving positive charge 
D)  the velocity of a moving negative charge 
E)  none of the above 
A)  the magnetic force on a moving positive charge 
B)  the magnetic force on a moving negative charge 
C)  the velocity of a moving positive charge 
D)  the velocity of a moving negative charge 
E)  none of the above E

Question 4

A uniform magnetic field is directed into the page. A charged particle, moving in the plane of the page, follows a clockwise spiral of decreasing radius as shown. A reasonable explanation is:

Accepted Answer

A)  the charge is positive and slowing down 
B)  the charge is negative and slowing down 
C)  the charge is positive and speeding up 
D)  the charge is negative and speeding up 
E)  none of the above 
A)  the charge is positive and slowing down 
B)  the charge is negative and slowing down 
C)  the charge is positive and speeding up 
D)  the charge is negative and speeding up 
E)  none of the above

Question 5

An electron enters a region of uniform perpendicular   fields. It is observed that the velocity   of the electron is unaffected. A possible explanation is:

Accepted Answer

A)    is parallel to   and has magnitude E/B 
B)    is parallel to   
C)    is perpendicular to both   and has magnitude B/E 
D)    is perpendicular to both   and has magnitude E/B 
E)  the given situation is impossible 
A)    is parallel to   and has magnitude E/B 
B)    is parallel to   
C)    is perpendicular to both   and has magnitude B/E 
D)    is perpendicular to both   and has magnitude E/B 
E)  the given situation is impossible

Question 6

A current is clockwise around the outside edge of this page and a uniform magnetic field is directed parallel to the page, from left to right. If the magnetic force is the only force acting on the page, the page will turn so the right edge:

Accepted Answer

A)  moves toward you 
B)  moves away from you 
C)  moves to your right 
D)  moves to your left 
E)  does not move 
A)  moves toward you 
B)  moves away from you 
C)  moves to your right 
D)  moves to your left 
E)  does not move

Question 7

An electron and a proton are both initially moving with the same speed and in the same direction at 90˚ to the same uniform magnetic field. They experience magnetic forces, which are initially:

Accepted Answer

A)  identical 
B)  equal in magnitude but opposite in direction 
C)  in the same direction and differing in magnitude by a factor of 1840 
D)  in opposite directions and differing in magnitude by a factor of 1840 
E)  equal in magnitude but perpendicular to each other 
A)  identical 
B)  equal in magnitude but opposite in direction 
C)  in the same direction and differing in magnitude by a factor of 1840 
D)  in opposite directions and differing in magnitude by a factor of 1840 
E)  equal in magnitude but perpendicular to each other

Question 8

An electron is launched with velocity   in a uniform magnetic field   The angle $\theta$between   is between 0 and 90o. As a result, the electron follows a helix, its velocity vector   returning to its initial value in a time interval of:

Accepted Answer

A)  2πm/eB 
B)  2πmv/eB 
C)  2πmv sin$\theta$/eB 
D)  2πmv cos$\theta$/eB 
E)  none of these 
A)  2πm/eB 
B)  2πmv/eB 
C)  2πmv sin$\theta$/eB 
D)  2πmv cos$\theta$/eB 
E)  none of these

Question 9

A proton (charge e), traveling perpendicular to a magnetic field, experiences the same force as an alpha particle (charge 2e) which is also traveling perpendicular to the same field. The ratio of their speeds, vproton/valpha is:

Accepted Answer

A)  0.5 
B)  1 
C)  2 
D)  4 
E)  8 
A)  0.5 
B)  1 
C)  2 
D)  4 
E)  8

Question 10

An electron (charge = -1.6 *10-19C) is moving at 3 *105 m/s in the positive x direction. A magnetic field of 0.8 T is in the positive z direction. The magnetic force on the electron is:

Accepted Answer

A)  0 
B)  4 * 10-14 N in the positive z direction 
C)  4 *10-14 N in the negative z direction 
D)  4 * 10-14 N in the positive y direction 
E)  4 * 10-14 N in the negative y direction 
A)  0 
B)  4 * 10-14 N in the positive z direction 
C)  4 *10-14 N in the negative z direction 
D)  4 * 10-14 N in the positive y direction 
E)  4 * 10-14 N in the negative y direction

Question 11

Units of a magnetic field might be:

Accepted Answer

A)  C.m/s 
B)  C.s/m 
C)  C/kg 
D)  kg/C.s 
E)  N/C.m 
A)  C.m/s 
B)  C.s/m 
C)  C/kg 
D)  kg/C.s 
E)  N/C.m

Question 12

The magnetic force on a charged particle is in the direction of its velocity if:

Accepted Answer

A)  it is moving in the direction of the field 
B)  it is moving opposite to the direction of the field 
C)  it is moving perpendicular to the field 
D)  it is moving in some other direction 
E)  never 
A)  it is moving in the direction of the field 
B)  it is moving opposite to the direction of the field 
C)  it is moving perpendicular to the field 
D)  it is moving in some other direction 
E)  never

Question 13

An ion with a charge of +3.25*10−19 C is in region where a uniform electric field of 5 * 104. V/m is perpendicular to a uniform magnetic field of 0.8 T. If its acceleration is zero then its speed must be:

Accepted Answer

A)  0 
B)  1.6 * 104 m/s 
C)  4.0 * 105 m/s 
D)  6.3 * 105 m/s 
E)  any value but 0 
A)  0 
B)  1.6 * 104 m/s 
C)  4.0 * 105 m/s 
D)  6.3 * 105 m/s 
E)  any value but 0

Question 14

The units of magnetic dipole moment are:

Accepted Answer

A)  ampere 
B)  ampere .meter 
C)  ampere .meter2 
D)  ampere/meter 
E)  ampere/meter2 
A)  ampere 
B)  ampere .meter 
C)  ampere .meter2 
D)  ampere/meter 
E)  ampere/meter2

Question 15

The direction of the magnetic field in a certain region of space is determined by firing a test charge into the region with its velocity in various directions in different trials. The field direction is:

Accepted Answer

A)  one of the directions of the velocity when the magnetic force is zero 
B)  the direction of the velocity when the magnetic force is a maximum 
C)  the direction of the magnetic force 
D)  perpendicular to the velocity when the magnetic force is zero 
E)  none of the above 
A)  one of the directions of the velocity when the magnetic force is zero 
B)  the direction of the velocity when the magnetic force is a maximum 
C)  the direction of the magnetic force 
D)  perpendicular to the velocity when the magnetic force is zero 
E)  none of the above

Question 16

The diagrams show five possible orientations of a magnetic dipole   in a uniform magnetic field   For which of these does the magnetic torque on the dipole have the greatest magnitude?

Accepted Answer

A)  I 
B)  II 
C)  III 
D)  IV 
E)  V 
A)  I 
B)  II 
C)  III 
D)  IV 
E)  V

Question 17

J. J. Thomson's experiment, involving the motion of an electron beam in mutually perpendicular   fields, gave the value of:

Accepted Answer

A)  mass of electron 
B)  charge of electron 
C)  Earth's magnetic field 
D)  charge/mass ratio for electron 
E)  Avogadro's number 
A)  mass of electron 
B)  charge of electron 
C)  Earth's magnetic field 
D)  charge/mass ratio for electron 
E)  Avogadro's number

Question 18

An electron is travelling in the positive x direction. A uniform electric field   is in the negative y direction. If a uniform magnetic field with the appropriate magnitude and direction also exists in the region, the total force on the electron will be zero. The appropriate direction for the magetic field is:

Accepted Answer

A)  the positive y direction 
B)  the negative y direction 
C)  into the page 
D)  out of the page 
E)  the negative x direction 
A)  the positive y direction 
B)  the negative y direction 
C)  into the page 
D)  out of the page 
E)  the negative x direction

Question 19

An electron travels due north through a vacuum in a region of uniform magnetic field   that is also directed due north. It will:

Accepted Answer

A)  be unaffected by the field 
B)  speed up 
C)  slow down 
D)  follow a right-handed corkscrew path 
E)  follow a left-handed corkscrew path 
A)  be unaffected by the field 
B)  speed up 
C)  slow down 
D)  follow a right-handed corkscrew path 
E)  follow a left-handed corkscrew path

Question 20

A uniform magnetic field is in the positive z direction. A positively charged particle is moving in the positive x direction through the field. The net force on the particle can be made zero by applying an electric field in what direction?

Accepted Answer

A)  Positive y 
B)  Negative y 
C)  Positive x 
D)  Negative x 
E)  Positive z 
A)  Positive y 
B)  Negative y 
C)  Positive x 
D)  Negative x 
E)  Positive z

Exam 28: Magnetic Fields

In the formula

A loop of current-carrying wire has a magnetic dipole moment of 5 *10-4 A .m2. The moment initially is aligned with a 0.5-T magnetic filed.To rotate the loop so its dipole momentt is perpendicular to the field and hold it in that orentation, you must do work of:

At any point the magnetic field lines are in the direction of:

A uniform magnetic field is directed into the page. A charged particle, moving in the plane of the page, follows a clockwise spiral of decreasing radius as shown. A reasonable explanation is:

An electron enters a region of uniform perpendicular fields. It is observed that the velocity of the electron is unaffected. A possible explanation is:

A current is clockwise around the outside edge of this page and a uniform magnetic field is directed parallel to the page, from left to right. If the magnetic force is the only force acting on the page, the page will turn so the right edge:

An electron and a proton are both initially moving with the same speed and in the same direction at 90˚ to the same uniform magnetic field. They experience magnetic forces, which are initially:

An electron is launched with velocity in a uniform magnetic field The angle θ\thetaθ between is between 0 and 90o. As a result, the electron follows a helix, its velocity vector returning to its initial value in a time interval of:

A proton (charge e), traveling perpendicular to a magnetic field, experiences the same force as an alpha particle (charge 2e) which is also traveling perpendicular to the same field. The ratio of their speeds, vproton/valpha is:

An electron (charge = -1.6 *10-19C) is moving at 3 *105 m/s in the positive x direction. A magnetic field of 0.8 T is in the positive z direction. The magnetic force on the electron is:

Units of a magnetic field might be:

The magnetic force on a charged particle is in the direction of its velocity if:

An ion with a charge of +3.25*10−19 C is in region where a uniform electric field of 5 * 104. V/m is perpendicular to a uniform magnetic field of 0.8 T. If its acceleration is zero then its speed must be:

The units of magnetic dipole moment are:

The direction of the magnetic field in a certain region of space is determined by firing a test charge into the region with its velocity in various directions in different trials. The field direction is:

The diagrams show five possible orientations of a magnetic dipole in a uniform magnetic field For which of these does the magnetic torque on the dipole have the greatest magnitude?

J. J. Thomson's experiment, involving the motion of an electron beam in mutually perpendicular fields, gave the value of:

An electron travels due north through a vacuum in a region of uniform magnetic field that is also directed due north. It will:

A uniform magnetic field is in the positive z direction. A positively charged particle is moving in the positive x direction through the field. The net force on the particle can be made zero by applying an electric field in what direction?

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A loop of current-carrying wire has a magnetic dipole moment of 5 *10^-⁴ A .m². The moment initially is aligned with a 0.5-T magnetic filed.To rotate the loop so its dipole momentt is perpendicular to the field and hold it in that orentation, you must do work of:

A proton (charge e), traveling perpendicular to a magnetic field, experiences the same force as an alpha particle (charge 2e) which is also traveling perpendicular to the same field. The ratio of their speeds, v_proton/v_alpha is:

An electron (charge = -1.6 10^-¹⁹C) is moving at 3 10⁵ m/s in the positive x direction. A magnetic field of 0.8 T is in the positive z direction. The magnetic force on the electron is:

An ion with a charge of +3.2510⁻¹⁹ C is in region where a uniform electric field of 5 10^4.V/m is perpendicular to a uniform magnetic field of 0.8 T. If its acceleration is zero then its speed must be: