Deck 10: Magnetism and Electromagnetism

Question 1

Induced voltage is directly proportional to the relative motion between a conductor and a magnetic field.

Answer 1

True

Question 2

Magnetic fields can exert forces without objects physically touching.

Answer 2

True

Question 3

A Tesla is equal to a meter per Weber.

Answer 3

False

Question 4

If the current flow was visualized going into this page, the magnetic field would be drawn clockwise around the conductor.

Question 5

The ease with which domains align and a magnetic field is established, in a given material, is called the material's:

A) magnetomotive force
B) retentivity
C) permeability
D) reluctance

Question 6

A group of magnetic force lines going from the north pole of a magnet to the south pole is called:

A) electromagnetism
B) magnetic flux
C) force energy
D) permeability

Question 7

Magnetomotive force is:

A) directly proportional to the number of turns in the coil, and inversely proportional to the current through the coil.
B) directly proportional to the number of turns in the coil, and directly proportional to the current through the coil.
C) inversely proportional to the number of turns in the coil, and inversely proportional to the current through the coil.
D) inversely proportional to the number of turns in the coil, and directly proportional to the current through the coil.

Question 8

The amount of magnetomotive force is inversely proportional to the amount of current flow.

Question 9

Magnetic flux lines are never continuous outside of the magnet.

Question 10

The right hand rule is used for current-carrying conductors using electron flow.

Question 11

An example of an electromagnetic device is:

A) the relay
B) a tape recording head
C) the loudspeaker
D) the solenoid
E) all of the above

Question 12

What constitutes an electromagnet?

A) a core material with high reluctance with a coil of wire around it
B) a core material that can be easily magnetized with a coil of wire around it
C) a permanent magnet with a coil around it
D) a permanent magnet

Question 13

There is 1.5 A of current through a coil consisting of 8 turns, what is the magnetomotive force mmF)?

A) 5.33 ampere-turns At)
B) 9.5 ampere-turns At)
C) 12 ampere-turns At)
D) 6.5 ampere-turns At)

Question 14

What is the amount of flux in an 8-turn coil with 1.5 A of current if the reluctance is .04 x 106 At/Wb?

A) 150 µWb
B) 300 µWb
C) 0.48 µWb
D) 1.24 µWb

Question 15

Materials that can be magnetized are called ferromagnetic.

Question 16

Permanent magnets are characterized by the fact that:

A) they lose their magnetism very quickly.
B) they produce an electrostatic field.
C) their magnetic domains are aligned north-to-south.
D) their magnetic domains are randomly oriented.

Question 17

The S.I. is the unit of magnetic flux.

A) Maxwell
B) Weber
C) Tesla
D) reluctance

Question 18

A permanent magnet is basically a coil of wire wound around a magnetic core.

Question 19

The symbol for flux density is:

A) O
B) A
C) B
D) T

Question 20

Unlike magnetic poles attract each other, and like magnetic poles repel each other.

Question 21

Relative permeability of a magnetic material is a ratio of its:

A) absolute permeability to that of a vacuum
B) field intensity to its field density.
C) flux lines to its ampere-turns
D) area to its field density.

Question 22

According to Faraday's law, if the rate of flux change quadruples, what happens to the induced voltage?

A) It quadruples
B) It doubles.
C) It increases by a factor of eight
D) It halves.

Question 23

Another name for a hysteresis loop is:

A) field intensity
B) magnetomotive force
C) the B-H curve
D) flux density

Question 24

An example of an electromagnetic device that also uses a permanent magnet is:

A) the relay
B) a tape recording head
C) the solenoid
D) the loudspeaker
E) all of the above

Question 25

Calculate the induced voltage across a coil with 150 turns that is being cut by a magnetic field that is changing at a rate of 7 Wb/s.

A) 105 V
B) 1050 V
C) 1.05 V
D) 10.5 V

Question 26

Magnetic flux lines travel from:

A) north to south inside the magnet
B) north to south outside the magnet.
C) south to north outside the magnet
D) higher flux areas to lower flux areas

Question 27

Ferrites are:

A) low electrical resistance, high permeability materials.
B) high electrical resistance, high permeability materials.
C) paramagnetic materials.
D) diamagnetic materials.

Question 28

The force between carrying current parallel conductors:

A) is one of repulsion for the same direction of current flow.
B) is one of attraction for the same direction of current flow.
C) is cancelled no matter what the direction of current flow.
D) is neutral because the force fields from each conductor cancel each other out.

Question 29

The ability of a material to maintain a magnetized state without the presence of a magnetizing force is called:

A) retentivity
B) permeability
C) residual magnetism
D) reluctance

Question 30

Reluctance varies:

A) directly with its permeability
B) directly with its area.
C) inversely with its permeability
D) inversely with its length.

Question 31

What is the mmf of a material whose magnetic flux is equal to 670 microwebers with a reluctance of
44.8 × 103 At/Wb?

A) 30 At
B) 20 At
C) 40 At
D) 10 At

Question 32

The opposition to magnetic flux line flow is called:

A) retention
B) reluctance
C) Webers per meter
D) permeability.

Question 33

Faraday's law states that the:

A) direction of induced voltage produces an opposition.
B) emf depends on the rate of cutting flux.
C) direction of an induced current produces an aiding effect.
D) emf is related to the direction of current.

Question 34

The most common movement for analog meters is the:

A) electrodynamometer
B) d'Arsonval movement
C) iron-vane movement
D) hot wire movement

Question 35

The magnetizing force H) is not dependent on which of following?

A) the length of the material
B) the number of turns
C) the type of material
D) the amount of current flow

Question 36

Which of the following statements about flux lines is not correct?

A) They are continuous.
B) They never cross each other.
C) Magnetic flux flows from the north pole to the south pole within the magnet.
D) They flow in the shortest and/or easiest path.

Question 37

The B-H curve plots:

A) flux intensity versus flux density
B) permeability versus reluctance.
C) retentivity versus saturation
D) flux density versus magnetizing force.

Question 38

The Greek symbol is used to indicate the of a material in relation to flux lines.

A) µ, permeability
B) 1, reluctance
C) fi, Webers
D) 6, Gauss

Question 39

Magnetomotive force in an electromagnet is increased by:

A) increasing coil turns
B) decreasing the voltage
C) decreasing permeability
D) increasing coil length

Question 40

Magnetizing force "H," is measured in:

A) ampere-turns per meter
B) ampere-turns per Weber.
C) number of turns per square meter
D) Webers per square meter.

Question 41

Calculate the reluctance of a 4-meter long toroidal coil made of low-carbon steel with an inner radius of 1.75 cm and an outer radius of 2.25 cm. The permeability of the steel is 2 × 10-4 Wb/At - m.

A) 2.29 × 106 At/Wb
B) 4.03 × 105 At/Wb
C) 1.96 × 10-5 At/Wb
D) 31.9 × 106 At/Wb