Deck 4: Electromagnetism

Question 1

Electrons move downward in a vertical wire.The direction of the associated magnetic field directly around the wire is

A)clockwise.
B)counterclockwise.
C)in the direction of the electron flow.
D)opposite to the conventional current.

Answer 1

counterclockwise.

Question 2

The inherent power loss of electrical conduction through solid wire conductors

A)is minimized with higher voltage transmission.
B)has no relationship with current flow.
C)results from space charge.
D)is lower with current flow rather than electron flow.

Answer 2

is minimized with higher voltage transmission.

Question 3

The efficiency of a transformer is not affected by

A)eddy current loss.
B)power loss.
C)hysteresis loss.
D)the transformer turns ratio.

Answer 3

the transformer turns ratio.

Question 4

A generator is a device that converts

A)electrical energy to thermal energy.
B)thermal energy to electrical energy.
C)mechanical energy to electrical energy.
D)electrical energy to mechanical energy.

Question 5

The charge carriers are considered to be a negative in a/an

A)diode.
B)triode.
C)n-type semiconductor.
D)p-type semiconductor.

Question 6

A transformer with more secondary windings than primary windings

A)has a greater secondary voltage.
B)is a step-down transformer.
C)has a greater power output than input.
D)has a higher power loss.

Question 7

The magnitude of force felt by a moving charge through a magnetic field would be least if the charge were

A)moving directly into the magnetic field.
B)moving directly away from the magnetic field.
C)moving at a right angle to the magnetic field.
D)both a and b

Question 8

A bar magnet and a wire loop move with the same linear velocity and direction.What is the voltage induced in the wire?

A)maximum when the wire and magnetic flux are parallel
B)directly proportional to their velocities
C)inversely proportional to the velocities
D)zero

Question 9

A simple DC generator has essentially the same construction as an AC generator except that a DC generator employs the use of

A)slip rings.
B)a commutator.
C)brushes.
D)an armature.

Question 10

American generators operate at

A)220 V.
B)120 AC.
C)60 Hz.
D)30 A.

Question 11

How many times does an AC current change direction in a single minute?

A)30
B)60
C)120
D)7,200

Question 12

A diode electron tube such as a valve tube

A)is used for amplification.
B)has a negatively charged anode.
C)is used to vary the primary voltage.
D)can be used for rectification.

Question 13

An induced current in a wire loop

A)results from a constant magnetic flux.
B)can result only from an alternately expanding and contracting magnetic field.
C)is in such a direction that its effects oppose the change producing the current.
D)always decreases when the magnetic flux decreases.

Question 14

A magnetic field is produced by

A)electric charges at rest.
B)electric charges in motion.
C)permanent magnets only.
D)electric charges both at rest and in motion.

Question 15

A motor is a device that converts

A)thermal energy into electrical energy.
B)electrical energy into mechanical energy.
C)electrical energy into electromagnetic energy.
D)mechanical energy into electrical energy.

Question 16

The process of electrons being emitted from heated metallic surfaces is called

A)thermionic emission.
B)electrolysis.
C)electroplating.
D)potential difference.

Question 17

For a simple AC generator, the value of the induced voltage in the armature loop is maximum when the orientation of the armature as compared to the magnetic field is

A)at a node.
B)45 degrees.
C)90 degrees.
D)180 degrees.

Question 18

An alternately expanding and contracting magnetic field is produced by

A)a stationary magnet.
B)a steady current flowing in a wire.
C)a battery.
D)none of the above

Question 19

The magnetic flux through a wire loop

A)requires a time-varying magnetic field.
B)is maximum when the plane of the loop is perpendicular to the magnetic field.
C)increases as the magnetic field decreases.
D)stays fixed in orientation regardless of electron flow.

Question 20

A rectifier

A)refers to a type of electromagnetic device.
B)changes electron flow to current flow.
C)converts DC to AC.
D)converts AC to DC.

Question 21

List the three ways to induce an electromagnetic field.

Question 22

Match the following selections as they relate to the process of rectification.
also called SCR

A)semiconductor
B)diode
C)p-type material
D)n-type material
E)thyristor
F)valve tube
G)arsenic
H)gallium

Question 23

An electrical device that is designed to store charge momentarily after charging is a/an

A)battery.
B)capacitor.
C)thyristor.
D)dielectric.

Question 24

When using alternating current,

A)resistance is calculated as impedance (Z).
B)electrical production can be graphically expressed as a sinusoidal wave.
C)it must be rectified prior to the high voltage transformer.
D)both a and b

Question 25

All of the following are true of transformers EXCEPT:

A)They have no moving parts.
B)They work on the principle of mutual induction.
C)They work most efficiently on pulsating DC.
D)They are designed to regulate voltage.

Question 26

Solid state rectifiers use semiconductor technology.This valuable technology has led to the term "Silicon Valley" and is commonly associated with the computer and transistor industries.The core material for semiconductors is silicon which is intentionally combined with impurities using the elements of arsenic, gallium and boron.This process is termed "doping" and is used to control electron flow through an n-p interface or junction.How is arsenic used to affect semiconductor conductance?

Question 27

The material of choice for semiconductors is

A)silicon.
B)carbon.
C)gadolinium.
D)ferrous iron.

Question 28

Match the following selections as they relate to the process of rectification.
p-type material sandwiched with n-type material

A)semiconductor
B)diode
C)p-type material
D)n-type material
E)thyristor
F)valve tube
G)arsenic
H)gallium

Question 29

All of the following are true of autotransformers EXCEPT:

A)They are considered a variable transformer.
B)The primary and secondary coils are in series.
C)The primary and secondary windings share a common coil.
D)They are effective in controlling voltage on the high voltage side of the circuit.

Question 30

Conventional current flows

A)from cathode to anode.
B)from anode to cathode.
C)in either direction.
D)in the same direction as the electron flow.

Question 31

Match the following selections as they relate to the process of rectification.
designed to permit electron flow in one direction only

A)semiconductor
B)diode
C)p-type material
D)n-type material
E)thyristor
F)valve tube
G)arsenic
H)gallium

Question 32

The design of an x-ray tube requires that electron flow through it is in a single direction or phase.If alternating current were supplied to the x-ray tube at high voltage, what would be the result?

Question 33

All of the following are true of induction motors EXCEPT:

A)They use multiphase current and can turn at varying rpm.
B)Motor power can be regulated by the characteristics of the electromagnets that make up the stator.
C)Their design is inherently weak with regard to power.
D)They are used to spin the x-ray tube anode disk.

Question 34

Match the following selections as they relate to the process of rectification.
an electron doper to improve conductance

A)semiconductor
B)diode
C)p-type material
D)n-type material
E)thyristor
F)valve tube
G)arsenic
H)gallium

Question 35

The magnitude of an induced electromagnetic field depends on what four factors?

Question 36

If a transformer is supplied with 16 volts and 4 amperes, the output current from this transformer with an output voltage of 1200 volts would be

A)24 volts.
B)0.02 amperes.
C)480 amperes.
D)800 amperes.

Question 37

Match the following selections as they relate to the process of rectification.
obsolete type of rectification technology

A)semiconductor
B)diode
C)p-type material
D)n-type material
E)thyristor
F)valve tube
G)arsenic
H)gallium

Question 38

Match the following selections as they relate to the process of rectification.
atomic element that creates electron "holes"

A)semiconductor
B)diode
C)p-type material
D)n-type material
E)thyristor
F)valve tube
G)arsenic
H)gallium

Question 39

The turns ratio of a transformer is determined by the

A)size of the wire.
B)type of wire.
C)number of windings.
D)space between the transformer sides.

Question 40

A stator consists of

A)bars of copper around an iron core.
B)commutator rings.
C)a rotor.
D)electromagnets.

Question 41

Match the terms relating to magnetism with the correct choice.
cobalt

A)magnetic flux
B)spin magnetic moment
C)tesla
D)electromagnet
E)permeability
F)retentivity
G)paramagnetic
H)ferromagnetic

Question 42

Match the terms relating to magnetism with the correct choice.
resistance to demagnetization

A)magnetic flux
B)spin magnetic moment
C)tesla
D)electromagnet
E)permeability
F)retentivity
G)paramagnetic
H)ferromagnetic

Question 43

Match the terms relating to magnetism with the correct choice.
10,000 gauss

A)magnetic flux
B)spin magnetic moment
C)tesla
D)electromagnet
E)permeability
F)retentivity
G)paramagnetic
H)ferromagnetic

Question 44

Match the terms relating to magnetism with the correct choice.
electron rotation on an axis

A)magnetic flux
B)spin magnetic moment
C)tesla
D)electromagnet
E)permeability
F)retentivity
G)paramagnetic
H)ferromagnetic

Question 45

Match the terms relating to magnetism with the correct choice.
ratio between field strength and area

A)magnetic flux
B)spin magnetic moment
C)tesla
D)electromagnet
E)permeability
F)retentivity
G)paramagnetic
H)ferromagnetic

Question 46

Match the terms relating to magnetism with the correct choice.
electrical coil with ferrous core

A)magnetic flux
B)spin magnetic moment
C)tesla
D)electromagnet
E)permeability
F)retentivity
G)paramagnetic
H)ferromagnetic