3A2 Chapter 07 Flashcards
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
E) 1,2,3,4
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
D) 1,4
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 t neutron
B) negative to positive
The free valence electrons of a conductor, when connected to the poles of a battery will move toward a ____
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
C) the positive pole
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
C) 1,4
What practical unit is used to represent resistance?
A) watt B) amp C) ohm D) microhms E) Henry
C) ohm
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 outlet
C) in motion
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, type of material, length and temperature
B) type of material, length, diameter and temperature
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
C) current
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
C) distorts
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 torque produced on it D) turn counter clockwise E) straighten itself out
C) have torque produced on it
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) EMF
A magnetic field is always considered to travel from ____
A) positive to negative B) negative to positive C) upwards to downwards D) south to north E) north to south
E) north to south
In a generator, the direction of the induced emf can be determined by applying Flemming’s ______ hand rule
A) back B) two C) inverse D) left E) right
E) right
If the current in the conductor is reversed, or if the direction of the main field is reversed, the the force on the conductor will be reversed
A) true
B) false
A) true
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) induce a torque D) generate a DC current E) generate a DC voltage
C) induce a torque
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) voltage
The armature of a DC generator is wrapped with field windings
A) true
B) false
A) true
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
D) kept comparatively small
What is the yoke in a DC machine usually made of?
A) steel B) copper C) aluminum D) insulation E) semi conducting materials
A) steel
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
E) the bearing housings
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
D) soft iron or mild steel laminations
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
The displacement between the centres 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
The displacement between centres 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
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
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
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
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
Armature reaction _____ the main field
A) increases B) decreases C) reverses D) distorts E) restores
D) distorts
Interpoles carry ______ current
A) field B) load C) flux D) armature E) stator
D) armature
Interpoles are connected in series with the ______
A) field coils B) load C) armature D) field poles E) stator
C) armature
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
The separately excited generator has a _______ load characteristic
A) rising B) level C) falling D) series E) parallel
C) falling
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
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
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
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
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
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
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 field flux, the speed can become dangerously high. For the reason the series motor must never be operated without a load
A) true
B) false
A) true
The behaviour 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
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
Some of the characteristics of the series direct current motor include:
1) a small current at no load conditions
2) the danger of over speed 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
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
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
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
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
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
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
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
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
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
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%
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
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 coloured glass
E) should have higher current ratings than the line system
A) should have higher voltage ratings than the line system
