Question 1

A static magnetic field CANNOT:

Accepted Answer

A)  exert a force on a charge 
B)  accelerate a charge 
C)  change the momentum of a charge 
D)  change the kinetic energy of a charge 
E)  exist 
A)  exert a force on a charge 
B)  accelerate a charge 
C)  change the momentum of a charge 
D)  change the kinetic energy of a charge 
E)  exist

Question 2

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)  north 
D)  south 
E)  west 
A)  zero 
B)  up 
C)  north 
D)  south 
E)  west

Question 3

At one instant an electron is moving in the positive x direction along the x axis in a region where there is a uniform magnetic field in the positive z direction. When viewed from a point on the positive z axis, it subsequent motion is:

Accepted Answer

A)  straight ahead 
B)  counterclockwise around a circle in the xy plane 
C)  clockwise around a circle in the xy plane 
D)  in the positive z direction 
E)  in the negative z direction 
A)  straight ahead 
B)  counterclockwise around a circle in the xy plane 
C)  clockwise around a circle in the xy plane 
D)  in the positive z direction 
E)  in the negative z direction

Question 4

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

Question 5

An ion with a charge of +3.2 *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 m/s 
B)  1.6 * 10-5 m/s 
C)  4.0 *105 m/s 
D)  6.3 *105 m/s 
E)  any value but 0 m/s 
A)  0 m/s 
B)  1.6 * 10-5 m/s 
C)  4.0 *105 m/s 
D)  6.3 *105 m/s 
E)  any value but 0 m/s

Question 6

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

Accepted Answer

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

Question 7

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 8

A cyclotron operates with a given magnetic field and at a given frequency. If R denotes the radius of the final orbit, the final particle energy is proportional to:

Accepted Answer

A)  1/R 
B)  R 
C)  R2 
D)  R3 
E)  R4 
A)  1/R 
B)  R 
C)  R2 
D)  R3 
E)  R4

Question 9

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 AF.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 AF.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 10

The magnetic torque exerted on a flat current-carrying loop of wire by a uniform magnetic field is:

Accepted Answer

A)  maximum when the plane of the loop is perpendicular to 
B)  maximum when the plane of the loop is parallel to 
C)  dependent on the shape of the loop for a fixed loop area 
D)  independent of the orientation of the loop 
E)  such as to rotate the loop around the magnetic field lines 
A)  maximum when the plane of the loop is perpendicular to 
B)  maximum when the plane of the loop is parallel to 
C)  dependent on the shape of the loop for a fixed loop area 
D)  independent of the orientation of the loop 
E)  such as to rotate the loop around the magnetic field lines

Question 11

An electron enters a region of uniform perpendicular and 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 and has magnitude B/E 
D)  is perpendicular to both and 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 and has magnitude B/E 
D)  is perpendicular to both and and has magnitude E/B 
E)  the given situation is impossible

Question 12

A charged particle is projected into a region of uniform, parallel, and 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 13

For a loop of current-carrying wire in a uniform magnetic field the potential energy is a minimum if the magnetic dipole moment of the loop is:

Accepted Answer

A)  in the same direction as the field 
B)  in the direction opposite to that of the field 
C)  perpendicular to the field 
D)  at an angle of 45 $\degree$ to the field 
E)  none of the above 
A)  in the same direction as the field 
B)  in the direction opposite to that of the field 
C)  perpendicular to the field 
D)  at an angle of 45 $\degree$ to the field 
E)  none of the above

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 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)  downward 
D)  upward 
E)  along its length 
A)  toward the magnet 
B)  away from the magnet 
C)  downward 
D)  upward 
E)  along its length

Question 16

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 magnetic 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 17

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 18

A beam of electrons is sent horizontally down the axis of a tube to strike a fluorescent screen at the end of the tube. On the way, the electrons encounter a magnetic field directed vertically downward. The spot on the screen will therefore be deflected:

Accepted Answer

A)  upward 
B)  downward 
C)  to the right as seen from the electron source 
D)  to the left as seen from the electron source 
E)  not at all 
A)  upward 
B)  downward 
C)  to the right as seen from the electron source 
D)  to the left as seen from the electron source 
E)  not at all

Question 19

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 20

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

Exam 28: Magnetic Fields

A static magnetic field CANNOT:

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

At one instant an electron is moving in the positive x direction along the x axis in a region where there is a uniform magnetic field in the positive z direction. When viewed from a point on the positive z axis, it subsequent motion is:

In the formula

An ion with a charge of +3.2 *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:

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

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

A cyclotron operates with a given magnetic field and at a given frequency. If R denotes the radius of the final orbit, the final particle energy is proportional to:

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:

The magnetic torque exerted on a flat current-carrying loop of wire by a uniform magnetic field is:

An electron enters a region of uniform perpendicular and 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, and fields. The force on the particle is:

For a loop of current-carrying wire in a uniform magnetic field the potential energy is a minimum if the magnetic dipole moment of the loop is:

The units of magnetic dipole moment are:

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

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:

A beam of electrons is sent horizontally down the axis of a tube to strike a fluorescent screen at the end of the tube. On the way, the electrons encounter a magnetic field directed vertically downward. The spot on the screen will therefore be deflected:

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:

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

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An ion with a charge of +3.2 10⁻¹⁹ 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: