Question 1

The diagram shows a straight wire carrying current i in a uniform magnetic field. The magnetic force on the wire is indicated by an arrow but the magnetic field is not shown. Of the following possibilities, the direction of the magnetic field is:

Accepted Answer

A)   to the right
B)   opposite the direction of 
C)   in the direction of 
D)   into the page
E)   out of the page E

Question 2

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 C

Question 3

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

Question 4

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

Question 5

A square loop of wire lies in the plane of the page and carries a current I as shown. There is a uniform magnetic field  parallel to the side MK as indicated. The loop will tend to rotate:

Accepted Answer

A)   about PQ with KL coming out of the page
B)   about PQ with KL going into the page
C)   about RS with MK coming out of the page
D)   about RS with MK going into the page
E)   about an axis perpendicular to the page

Question 6

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

Question 7

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

Question 8

The diagram shows a straight wire carrying a flow of electrons into the page. The wire is between the poles of a permanent magnet. The direction of the magnetic force exerted on the wire is:

Accepted Answer

A)    ↑\uparrow↑ 
B)    ↓\downarrow↓ 
C)    →\rightarrow→ 
D)    ←\leftarrow← 
E)   into the page

Question 9

The magnetic dipole moment of a current-carrying loop of wire is in the positive z direction. If a uniform magnetic field is in the positive x direction the magnetic torque on the loop is:

Accepted Answer

A)   0
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 10

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

Question 11

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

Question 12

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

Question 13

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

Question 14

In a certain mass spectrograph, an ion beam passes through a velocity filter consisting of mutually perpendicular fields  The beam then enters a region of another magnetic field  perpendicular to the beam. The radius of curvature of the resulting ion beam is proportional to:

Accepted Answer

A)   EB'/B
B)   EB/B'
C)   BB'/E
D)   B/EB'
E)   E/BB'

Question 15

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

Question 16

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

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

Question 18

The figure shows a uniform magnetic field  directed to the left and a wire carrying a current into the page. The magnetic force acting on the wire is:

Accepted Answer

A)   toward the top of the page
B)   toward the bottom of the page
C)   toward the left
D)   toward the right
E)   zero

Question 19

The current is from left to right in the conductor shown. The magnetic field is into the page and point S is at a higher potential than point T. The charge carriers are:

Accepted Answer

A)   positive
B)   negative
C)   neutral
D)   absent
E)   moving near the speed of light

Question 20

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 in the plane of the triangle and is perpendicular 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

Exam 28: Magnetic Fields

The diagram shows a straight wire carrying current i in a uniform magnetic field. The magnetic force on the wire is indicated by an arrow but the magnetic field is not shown. Of the following possibilities, the direction of the magnetic field is:

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:

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:

An ion with a charge of +3.25 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:

A square loop of wire lies in the plane of the page and carries a current I as shown. There is a uniform magnetic field parallel to the side MK as indicated. The loop will tend to rotate:

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:

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:

The magnetic dipole moment of a current-carrying loop of wire is in the positive z direction. If a uniform magnetic field is in the positive x direction the magnetic torque on the loop is:

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:

In the formula

Units of a magnetic field might be:

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

In a certain mass spectrograph, an ion beam passes through a velocity filter consisting of mutually perpendicular fields The beam then enters a region of another magnetic field perpendicular to the beam. The radius of curvature of the resulting ion beam is proportional to:

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:

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

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

The figure shows a uniform magnetic field directed to the left and a wire carrying a current into the page. The magnetic force acting on the wire is:

The current is from left to right in the conductor shown. The magnetic field is into the page and point S is at a higher potential than point T. The charge carriers are:

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 in the plane of the triangle and is perpendicular to the hypotenuse. The resultant magnetic force on the two sides has a magnitude of:

Exam 28: Magnetic Fields

The diagram shows a straight wire carrying current i in a uniform magnetic field. The magnetic force on the wire is indicated by an arrow but the magnetic field is not shown. Of the following possibilities, the direction of the magnetic field is:

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:

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:

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:

A square loop of wire lies in the plane of the page and carries a current I as shown. There is a uniform magnetic field parallel to the side MK as indicated. The loop will tend to rotate:

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:

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:

The diagram shows a straight wire carrying a flow of electrons into the page. The wire is between the poles of a permanent magnet. The direction of the magnetic force exerted on the wire is:

The magnetic dipole moment of a current-carrying loop of wire is in the positive z direction. If a uniform magnetic field is in the positive x direction the magnetic torque on the loop is:

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:

In the formula

Units of a magnetic field might be:

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

In a certain mass spectrograph, an ion beam passes through a velocity filter consisting of mutually perpendicular fields The beam then enters a region of another magnetic field perpendicular to the beam. The radius of curvature of the resulting ion beam is proportional to:

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:

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

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

The figure shows a uniform magnetic field directed to the left and a wire carrying a current into the page. The magnetic force acting on the wire is:

The current is from left to right in the conductor shown. The magnetic field is into the page and point S is at a higher potential than point T. The charge carriers are:

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 in the plane of the triangle and is perpendicular to the hypotenuse. The resultant magnetic force on the two sides has a magnitude of:

An ion with a charge of +3.25 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:

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: