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Ch. 7 Flashcards

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1
Q
  1. Resistance:
    1) Limits current flow
    2) Depends on material
    3) Depends on temperature
    4) Depends on dimensions
    a. 1, 3, 4
    b. 1, 2, 3
    c. 1, 2, 4
    d. 2, 3, 4
    e. 1, 2, 3, 4
A

e. 1, 2, 3, 4

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2
Q
  1. What practical unit is used to represent resistance?
    a. Watt
    b. Amp
    c. Ohm
    d. Microhms
    e. Henry
A

c. Ohm

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2
Q
  1. Conductive materials.
    1) Gain resistance while temperature rises while others lose resistance
    2) Have no resistance change with temperature change
    3) Always have resistance changing directly with temperature
    4) Can vary resistance directly or inversely with temperature
    a. 1, 3, 4
    b. 2, 3
    c. 2, 4
    d. 1, 4
    e. 1, 2, 3, 4
A

d. 1, 4

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3
Q
  1. Free valence electrons flow from _______ when connected to an electrical supply.
    a. positive to negative
    b. negative to positive
    c. positive to proton
    d. negative to proton
    e. positive to neutron
A

b. negative to positive

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4
Q
  1. When a loop of current carrying conductor is placed in a magnetic field, the wire loop will __________.
    a. turn clockwise
    b. generate a current
    c. have a torque produced on it
    d. turn counter-clockwise
    e. straightens itself out
A

c. have a torque produced on it

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4
Q
  1. An electrical source could be in the form of a:
    1) Battery
    2) Magnet
    3) Flux
    4) Generator
    a. 1, 2, 4
    b. 2, 3
    c. 1, 4
    d. 2, 3, 4
    e. 1, 2, 3, 4
A

c. 1, 4

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4
Q
  1. The free valence electrons of a conductor, when connected to the poles of a battery will move towards _____.
    a. both poles at the same time
    b. the negative pole
    c. the positive pole
    d. either or both poles, quite randomly
    e. the cathode
A

c. the positive pole

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4
Q
  1. When a current carrying conductor is placed in a magnetic field, the field produced by the conductor __________ the magnetic field between the poles.
    a. adds to
    b. subtracts from
    c. distorts
    d. crosses
    e. straightens
A

c. distorts

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5
Q
  1. The power source must maintain a potential difference _____________________.
    a. between two points
    b. across the emf
    c. across the short circuit
    d. within the load
    e. between the prime mover and generator
A

a. between two points

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5
Q
  1. The Electric current flow depends on the number of charges ___________________.
    a. between two points
    b. per second
    c. in motion
    d. as a potential
    e. per mechanical power output
A

c. in motion

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5
Q
  1. What factors determine the resistance of a conductor?
    a. Weight, length, diameter and temperature.
    b. Type of material, length, diameter and temperature.
    c. Weight, type of material, length and diameter.
    d. Weight, type of material, length, diameter and temperature.
    e. Weight, length, temperature and diameter.
A

b. Type of material, length, diameter and temperature.

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5
Q
  1. A conductor’s resistance to current flow is dependent on the following factors.
    a. Weight, length, diameter and temperature.
    b. Type of material, length, diameter and temperature.
    c. Weight, type of material, length and diameter.
    d. Weight, type of material, length, diameter and temperature.
    e. Weight, type of material, length and temperature.
A

b. Type of material, length, diameter and temperature.

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5
Q
  1. A magnetic field is always considered to travel from _____________.
    a. positive to negative
    b. negative to positive
    c. upward to downward
    d. south to north
    e. north to south
A

e. north to south

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5
Q
  1. In a magnetic circuit, the magnetic flux is the equivalent of electric _____________ in an electric circuit.
    a. voltage
    b. reluctance
    c. current
    d. resistance
    e. inductance
A

c. current

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6
Q
  1. In a generator, the direction of the induced emf can be determined by applying Fleming’s ______ Hand Rule.
    a. Back
    b. Two
    c. Inverse
    d. Left
    e. Right
A

e. Right

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6
Q
  1. If a conductor is moved relative to a magnetic field so as to “cut” the magnetic flux then an ________ will be induced in the conductor.
    a. emf
    b. current
    c. reluctance
    d. back emf
    e. inductance
A

a. emf

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6
Q
  1. The magneto motive force in a magnetic circuit has its equivalent in an electric circuit which is the _______.
    a. voltage
    b. magnetic flux
    c. electric current
    d. reluctance
    e. inductance
A

a. voltage

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6
Q
  1. When a current carrying conductor forming a loop is placed inside an external magnetic field, then the external field will cause the loop to______________.
    a. vibrate
    b. generate an AC current
    c. produce a torque
    d. generate a DC current
    e. generate a DC voltage
A

c. produce a torque

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6
Q
  1. If the current in the conductor is reversed, or if the direction of the main field is reversed, then the force on the conductor will be reversed.
    a. True
    b. False
A

a. True

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6
Q
  1. The armature of a DC generator is wrapped with field windings.
    a. True
    b. False
A

a. True

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7
Q
  1. The air gaps between the poles and the armature are _____________.
    a. filled with insulation
    b. subject to sparking
    c. increased with speed
    d. kept comparatively small
    e. to insulate the poles from the armature
A

d. kept comparatively small

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7
Q
  1. What should the end shields hold?
    a. The armature conductors at the ends of the armature.
    b. The field windings tightly to the field poles.
    c. The brushes in contact with the armature.
    d. The rotor and the armature together.
    e. The bearing housings.
A

e. The bearing housings.

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7
Q
  1. What is the armature core made of?
    a. Copper
    b. Copper laminations
    c. Hard steel laminations
    d. Soft iron or mild steel laminations
    e. Stainless steel laminations
A

d. Soft iron or mild steel laminations

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7
Q
  1. What is the yoke in a DC machine is usually made of?
    a. Steel
    b. Copper
    c. Aluminum
    d. Insulation
    e. Semi-conducting materials
7
822. The assembled armature core_____________. a. is wrapped with field windings b. has axial slots around its periphery c. contacts the brushes d. is constructed of hard-drawn copper bars e. is connected with the rotor
b. has axial slots around its periphery
8
823. The displacement between the centers of adjacent poles in an armature is ____________. a. one pole pitch b. 360 electrical degrees c. 180 mechanical degrees d. 90 electrical degrees e. 120 electrical degrees
a. one pole pitch
9
825. Neutral axis refers to? a. A position of the stator causing maximum sparking. b. A position of the stator causing minimum sparking. c. A position of the brushes causing minimum sparking. d. A position of the brushes causing maximum sparking. e. A position of the rotor causing minimum sparking.
c. A position of the brushes causing minimum sparking.
9
824. The displacement between the centers of adjacent poles in an armature are__________. a. 360 mechanical degrees b. 360 electrical degrees c. 180 mechanical degrees d. 180 electrical degrees e. 90 electrical degrees
d. 180 electrical degrees
10
826. With regard to the air gaps between the poles and the armature, such gaps must be ___________. a. filled with insulation b. kept large to prevent sparking c. increased with speed d. kept comparatively small e. kept large to prevent short circuiting
d. kept comparatively small
11
827. The torque produced by the armature conductors in a generator: 1) Increases with load 2) Decreases with load 3) Opposes the driving torque 4) Is load torque a. 1, 2, 3 b. 2, 3, 4 c. 1, 3, 4 d. 1, 2, 4 e. 1, 2, 3, 4
c. 1, 3, 4
12
829. Armature reaction _______________ the main field. a. increases b. decreases c. reverses d. distorts e. restores
d. distorts
12
828. The emf induced in a moving conductor depends on__________________. a. the load b. the back emf c. the temperature d. the counter current e. the speed of the moving conductor
e. the speed of the moving conductor
13
830. Interpoles carry _______________ current. a. field b. load c. flux d. armature e. stator
d. armature
14
831. Interpoles are connected in series with the ___________: a. field coils b. load c. armature d. field poles e. stator
c. armature
15
832. A way of overcoming armature reaction is by________________________. a. placing the brushes at the air gaps b. feeding AC current into the brushes c. inserting interpoles between the main poles d. reversing the brushes of the armature conductors e. correcting the positions of the poles
c. inserting interpoles between the main poles
16
833. The separately excited generator has a _______________ load characteristic. a. rising b. level c. falling d. series e. parallel
c. falling
17
835. The shunt generator has a no-load characteristic similar to that of the _________________ generator. a. series b. parallel c. compound d. separately-excited e. internally-excited
d. separately-excited
17
834. The manner in which the terminal voltage varies with a varying load current is called the ___________. a. percentage voltage regulation b. external characteristic c. internal characteristic d. no-load characteristic e. full-load characteristic
a. percentage voltage regulation
18
836. The three basic ways in which a self-excited generator can be connected are classified as: 1) Shunt generator 2) Compound generator 3) Series generator 4) Parallel generator a. 1, 3, 4 b. 2, 3, 4 c. 1, 2, 4 d. 1, 2, 3 e. 1, 2, 3, 4
d. 1, 2, 3
19
842. In a shunt motor, if the field becomes disconnected during operation the motor will _______________. a. over speed b. under speed c. slow down d. stop e. not change
a. over speed
19
837. In a series generator, the load current and generated voltage increase in inverse ratio to the load resistance until __________. a. the machine reaches maximum speed b. the magnetic saturation of the poles is reached c. the generator stops d. the generator reaches its maximum operating temperature e. the generator reaches its minimum operating temperature
b. the magnetic saturation of the poles is reached
20
838. For DC generators the nearer to zero the percentage voltage regulation is then _______________. a. the poorer the voltage regulation b. the greater the voltage regulation c. the higher the operating temperature possible d. the better the voltage regulation e. the lower the operating temperature possible
d. the better the voltage regulation
21
839. Excitation of the shunt field is controlled by? a. A regulating rheostat b. A mechanical governor c. A converter d. A long shunt e. A short shunt
a. A regulating rheostat
22
840. Series motor speed, a DC motor only takes the amount of current it requires to handle the load it is driving. Hence, the current is very low, and as the speed is inversely proportional to the field flux, the speed can become dangerously high. For this reason the series motor must never be operated without a load. a. True b. False
a. True
23
841. The behavior of the separately excited generator with regard to its load characteristic is that as load increases, its delivery voltage _______________. a. steeply rises b. remains constant c. slightly falls d. slightly fluctuates e. slightly above normal
b. remains constant
24
843. Some of the characteristics of the series direct current motor include: 1) A small current at no-load conditions 2) The danger of overspeed as the load is removed 3) The load current equals the excitation current 4) Its speed is directly proportional to field flux a. 1, 2, 3 b. 2, 3, 4 c. 1, 3, 4 d. 1, 2, 4 e. 1, 2, 3, 4
a. 1, 2, 3
25
844. Speed control is usually restricted to ________ motors: 1) Series 2) Shunt 3) Residual 4) Compounded a. 1, 2 b. 1, 3 c. 1, 4 d. 2, 3 e. 2, 4
e. 2, 4
26
845. Where high starting torques are required but the running load may be small the DC motor used would be the? a. Series b. Shunt c. Compound d. Under compounded e. Over compounded
c. Compound
27
846. In a shunt motor torque is proportional to _________________. a. the armature current b. the armature voltage c. the square of the armature current d. the length of the armature e. the diameter of the armature
a. the armature current
27
847. When high starting torque is desired a _____________ DC motor is best. a. Series b. Shunt c. Compound d. Three phase e. Manual start
a. Series
28
848. DC motors are restricted to a starting current of about _______ percent of full load current. a. 50 b. 100 c. 150 d. 200 e. 250
c. 150
29
849. The three-point starter for DC motors has connections for: 1) Line 2) Positive 3) Negative 4) Field 5) Armature a. 1, 2, 3, 4 b. 2, 3, 4, 5 c. 1, 3, 4, 5 d. 1, 2, 3 e. 1, 4, 5
e. 1, 4, 5
30
850. Where approximate constant speed is to be maintained between no-load and full-load the DC motor to use would be the______________. a. Series b. Shunt c. Compound d. Separately-excited e. Self-excited
b. Shunt
31
851. Where a large starting torque is of prime importance the DC motor to use would be the _________________. a. Series b. Long-shunt c. Short-shunt d. Compound e. Cumulative compound
a. Series
32
852. As the flux of a shunt motor remains constant its torque is ________________________. a. inversely proportional to armature current b. proportional to armature current c. increased d. decreased e. unchanged
b. proportional to armature current
33
853. The voltage drop at the armature of a shunt DC motor is a percentage that normally does not exceed ______. a. 0.05% b. 0.5% c. 0.9% d. 5.0% e. 50%
d. 5.0%
34
854. The most common type of industrial electrical generation is the _____________. a. single phase b. two phase c. three phase d. DC generators e. AC motors
c. three phase
35
855. When you are synchronizing an electrical generator and the synchronizing lamps are dark, you _________. a. should have higher voltage ratings than the line system b. have lower voltage rating c. have two or more lamps connected in parallel d. should have colored glass e. should have higher current ratings than the line system
a. should have higher voltage ratings than the line system
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