Question 1

An electron moves in the negative x direction, through a uniform magnetic field in the negative y direction. The magnetic force on the electron is:

Accepted Answer

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

Question 2

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

Question 3

A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A 0.7 T uniform magnetic field is parallel to the hypotenuse. The resultant magnetic force on the two sides has a magnitude of:

Accepted Answer

A)  0 
B)  0.21 N 
C)  0.30 N 
D)  0.41 N 
E)  0.51 N 
A)  0 
B)  0.21 N 
C)  0.30 N 
D)  0.41 N 
E)  0.51 N

Question 4

An electron is moving north in a region where the magnetic field is south. The magnetic force exerted on the electron is:

Accepted Answer

A)  zero 
B)  up 
C)  down 
D)  east 
E)  west 
A)  zero 
B)  up 
C)  down 
D)  east 
E)  west

Question 5

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 6

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 7

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 8

The figure shows the motion of electrons in a wire which is near the N pole of a magnet. The wire will be pushed:

Accepted Answer

A)  toward the magnet 
B)  away from the magnet 
C)  downwards 
D)  upwards 
E)  along its length 
A)  toward the magnet 
B)  away from the magnet 
C)  downwards 
D)  upwards 
E)  along its length

Question 9

A hydrogen atom that has lost its electron is moving east in a region where the magnetic field is directed from south to north. It will be deflected:

Accepted Answer

A)  up 
B)  down 
C)  north 
D)  south 
E)  not at all 
A)  up 
B)  down 
C)  north 
D)  south 
E)  not at all

Question 10

Electrons (mass m, charge -e) are accelerated from rest through a potential difference V and are then deflected by a magnetic field   that is perpendicular to their velocity. The radius of the resulting electron trajectory is:

Accepted Answer

A)    
B)    
C)    
D)    
E)  none of these 
A)    
B)    
C)    
D)    
E)  none of these

Question 11

A circular loop of wire with a radius of 20 cm lies in the xy plane and carries a current of 2 A, counterclockwise when viewed from a point on the positive z axis. Its magnetic dipole moment is:

Accepted Answer

A)  0.25 A . m2, in the positive z direction 
B)  0.25 A .m2, in the negative z direction 
C)  2.5 A .m2, in the positive z direction 
D)  2.5 A .m2, in the negative z direction 
E)  0.25 A . m2, in the xy plane 
A)  0.25 A . m2, in the positive z direction 
B)  0.25 A .m2, in the negative z direction 
C)  2.5 A .m2, in the positive z direction 
D)  2.5 A .m2, in the negative z direction 
E)  0.25 A . m2, in the xy plane

Question 12

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 13

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 14

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 15

A charged particle is projected into a region of uniform, parallel,   fields. The force on the particle is:

Accepted Answer

A)  zero 
B)  at some angle < 90° with the field lines 
C)  along the field lines 
D)  perpendicular to the field lines 
E)  unknown (need to know the sign of the charge) 
A)  zero 
B)  at some angle < 90° with the field lines 
C)  along the field lines 
D)  perpendicular to the field lines 
E)  unknown (need to know the sign of the charge)

Question 16

A magnetic field exerts a force on a charged particle:

Accepted Answer

A)  always 
B)  never 
C)  if the particle is moving across the field lines 
D)  if the particle is moving along the field lines 
E)  if the particle is at rest 
A)  always 
B)  never 
C)  if the particle is moving across the field lines 
D)  if the particle is moving along the field lines 
E)  if the particle is at rest

Question 17

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 18

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 19

You are facing a loop of wire which carries a clockwise current of 3.0 A and which surrounds an area of 5.8 10−2m2. The magnetic dipole moment of the loop is:

Accepted Answer

A)  3.0 A. m2, into the page 
B)  3.0 A . m2, out of the page 
C)  0.17 A .m2, into the page 
D)  0.17 A . m2, out of the page 
E)  0.17 A .m2, left to right 
A)  3.0 A. m2, into the page 
B)  3.0 A . m2, out of the page 
C)  0.17 A .m2, into the page 
D)  0.17 A . m2, out of the page 
E)  0.17 A .m2, left to right

Question 20

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

Exam 28: Magnetic Fields

An electron moves in the negative x direction, through a uniform magnetic field in the negative y direction. The magnetic force on the electron is:

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

A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A 0.7 T uniform magnetic field is parallel to the hypotenuse. The resultant magnetic force on the two sides has a magnitude of:

An electron is moving north in a region where the magnetic field is south. The magnetic force exerted on the electron is:

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:

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?

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:

The figure shows the motion of electrons in a wire which is near the N pole of a magnet. The wire will be pushed:

A hydrogen atom that has lost its electron is moving east in a region where the magnetic field is directed from south to north. It will be deflected:

Electrons (mass m, charge -e) are accelerated from rest through a potential difference V and are then deflected by a magnetic field that is perpendicular to their velocity. The radius of the resulting electron trajectory is:

A circular loop of wire with a radius of 20 cm lies in the xy plane and carries a current of 2 A, counterclockwise when viewed from a point on the positive z axis. Its magnetic dipole moment 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 enters a region of uniform perpendicular fields. It is observed that the velocity of the electron is unaffected. A possible explanation is:

A charged particle is projected into a region of uniform, parallel, fields. The force on the particle is:

A magnetic field exerts a force on a charged particle:

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:

The units of magnetic dipole moment are:

You are facing a loop of wire which carries a clockwise current of 3.0 A and which surrounds an area of 5.8 10−2m2. The magnetic dipole moment of the loop is:

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:

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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:

You are facing a loop of wire which carries a clockwise current of 3.0 A and which surrounds an area of 5.8 10⁻²m². The magnetic dipole moment of the loop is:

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: