Deck 15: Electromagnetism

Question 1

Reducing the residual induction is a method of demagnetization called ______________.

Answer 1

degaussing

Question 2

The physical motion from the forces of magnetic fields is called ______________ action.

Answer 2

motor

Question 3

An effect of a force in producing rotation is called ______________.

Answer 3

torque

Question 4

When magnetic flux moves, the motion of magnetic lines cutting across a conductor forces free electrons in the conductor to move and produce current by an action called ______________.

Question 5

______________ law is the basic principle for determining the direction of an induced voltage or current.

Question 6

In a ______________, motion must be supplied so that the flux and conductor can cut across each other to induce voltage across the ends of the conductor.

Question 7

A ______________ is an electromechanical device that operates switching contacts by electromagnetic induction.

Question 8

The movable arm of an electromechanical relay is called the ______________.

Question 9

Relay contacts may chatter if they are ______________.

Question 10

The magnetomotive force of a coil is ______________ proportional to both the current and the number of turns.

Question 11

When magnetic flux moves, the motion of magnetic lines cutting across a conductor forces free electrons in the conductor to move and produce current by an action called

A) conduction
B) induction
C) refraction
D) reflection

Question 12

To have electromagnetic induction, the conductor and the magnetic lines of flux must be

A) perpendicular to each other
B) adjacent to each other
C) completely separated from each other
D) separated by a magnetic shield

Question 13

Whose law or theorem is the basic principle for determining the direction of an induced voltage or current?

A) Maxwell
B) Gilbert
C) Lenz
D) Oersted

Question 14

For a coil, the induced voltage is increased by

A) the direction of current
B) the number of turns
C) using high resistance coil wire
D) shielding the coil

Question 15

What device operates because a current is supplied so that an associated magnetic field can react with the external flux to produce motion of the conductor?

A) Motor
B) Generator
C) Relay
D) Solenoid

Question 16

In what device is motion supplied so that the flux and conductor can cut across each other to induce voltage across the ends of the conductor?

A) Motor
B) Generator
C) Relay
D) Solenoid

Question 17

Which of the following does not help to determine the amount of induced voltage?

A) Amount of flux
B) Number of turns
C) Time rate of cutting
D) Size of conductor

Question 18

The symbol generally used for rate of change is

A) r
B) ?
C) d
D) ?

Question 19

An electromechanical device that operates switching contacts by electromagnetic induction is a

A) relay
B) solenoid
C) motor
D) generator

Question 20

The movable arm of an electromechanical relay is called the

A) coil
B) armature
C) contact
D) solenoid

Question 21

The minimum amount of relay coil voltage necessary to energize or operate a relay is called

A) contact voltage
B) drop voltage
C) pickup voltage
D) holding voltage

Question 22

What generally causes a relay to chatter?

A) Open coil
B) No voltage
C) Broken armature
D) Dirty contacts

Question 23

The mmf of a coil is

A) inversely proportional to the current and number of turns
B) directly proportional to the current and number of turns
C) inversely proportional to the current
D) inversely proportional to the number of turns

Question 24

The practical unit for magnetomotive force is the

A) gilbert
B) joule
C) maxwell
D) ampere-turn

Question 25

The SI abbreviation for ampere-turn is

A) A.T.
B) a x t
C) A
D) a-T

Question 26

What is the ampere-turns of mmf for a coil with 2000 turns and a 10 mA current?

A) 1 A · t
B) 10 A · t
C) 15 A · t
D) 20 A · t

Question 27

The cgs unit of magnetomotive force is the

A) gilbert
B) maxwell
C) oersted
D) joule

Question 28

The cgs unit for field intensity is the

A) gilbert
B) maxwell
C) oersted
D) joule

Question 29

What is often used to show how much flux density results from increasing the amount of field intensity?

A) Iron filings
B) AC voltmeter
C) Oscilloscope
D) B-H curve

Question 30

The effect of little change in flux density when the field intensity increases is called

A) reactance
B) reluctance
C) saturation
D) induction

Question 31

Hysteresis means

A) magnetize below
B) leading ahead
C) lagging behind
D) moving over

Question 32

Energy wasted in heat as the molecular dipoles lag the magnetizing force is called the

A) copper loss
B) IR loss
C) skin effect
D) hysteresis loss

Question 33

A coil of wire conductor with more than one turn is generally called a(n)

A) transformer
B) relay
C) electromagnet
D) solenoid

Question 34

A magnetic field is always associated with an electric current.

Question 35

For an electromagnet, the strength and intensity of the magnetic field does not depend on current flow or number of coil turns in a given length.

Question 36

The mmf of a coil is directly proportional to both the current and the number of turns.

Question 37

The SI abbreviation for ampere-turn is A.

Question 38

The ampere-turns of mmf specify the magnetizing force, but the intensity of the magnetic field depends on the length of the coil.

Question 39

The cgs unit for field intensity is the gilbert.

Question 40

The permeability of a material is similar in many respects to the conductivity in electric circuits.

Question 41

A B-H curve is often used to show how much flux density results from increasing the amount of field intensity.

Question 42

The effect of much change in flux density, when the field intensity increases, is called saturation.

Question 43

Hysteresis means lagging behind.

Question 44

Energy wasted in heat as the molecular dipoles lag the magnetizing force is called the hysteresis loss.

Question 45

Reducing the residual induction is a method of demagnetization called gaussing.

Question 46

The amp-clamp's probe senses the strength of the magnetic field set up by current in the wire and the meter deflection is proportional to the amount of current.

Question 47

When the magnetic lines of two fields are in the same direction, the lines of force aid each other, making the field stronger.

Question 48

A coil of wire with only one turn is generally called a solenoid.