Important Objective Questions On Rectifiers & Converters
1.With a motor converter it is possible to obtain D.C. voltage only upto
200-100 V
600�800 V
1000�1200 V
1700�2000 V
ANSWER : : 1700�2000 V
2.In a mercury arc rectifier positive ions are attracted towards
anode
cathode
shell bottom
mercury pool
ANSWER : : cathode
3.To produce cathode spot in a mercury arc rectifier
anode is heated
tube is evacuated
an auxiliary electrode is used
low mercury vapour pressures are used
ANSWER : : an auxiliary electrode is used
4.If cathode and anode connections in a mercury arc rectifier are inter changed
the rectifier will not operate
internal losses will be reduced
both ion and electron streams will move in the same direction
the rectifier will operate at reduced efficiency
ANSWER : : the rectifier will not operate
5.In which of the following appUcations, direct current is absolutely essential ?
Illumination
Electrolysis
Variable speed operation
Traction
ANSWER : : Electrolysis
6.The potential drop in the arc, in a mercury arc rectifier, varies
0.05 V to 0.2 V per cm length of the arc
0.5 V to 1.5 V per cm length of the arc
2 V to 3.5 V per cm length of the arc
none of the above
ANSWER : : none of the above
7.Which of the following is reversible in action ?
Motor generator set
Motor converter
Rotary converter
Any of the above
ANSWER : : Rotary converter
8.A rotary converter operates at a
low power factor
high power factor
zero power factor
none of the above
ANSWER : : high power factor
9.In a rotary converter armature currents are
d.c. only
a.c. only
partly a.c. and partly d.c.
partly a.c. and partly d.c.
ANSWER : In which of the following equipment direct current is needed ?
10.Which of the following AC. motors is usually used in large motor-generator sets?
Synchronous motor
Squirrel cage induction motor
Slip ring induction motor
Any of the above
ANSWER : : Synchronous motor
11.In a rotary converter I2R losses as compared to a D.C. generator of the same size will be
same
less
double
three times
ANSWER : : less
12.The internal efficiency of a mercury arc rectifier depends on
voltage only
current only
voltage and current
r.m.s. value of current
ANSWER : : voltage only
13.Normally, which of the following is used, when a large-scale conversion from AC. to D.C. power is required ?
Motor-generator set
Motor converter
Rotary converter
Mercury arc rectifier
ANSWER : : Mercury arc rectifier
14.The voltage drop at anode, in a mercury arc rectifier is due to
self restoring property of mercury
high ionization potential
energy spent in overcoming the electrostatic field
high temperature inside the rectifier
ANSWER : : energy spent in overcoming the electrostatic field
15.In a mercury pool rectifier, the voltage drop across its electrodes
is directly proportional to load
is inversely proportional to load
varies exponentially with the load current
is almost independent of load current
ANSWER : : is almost independent of load current
16.Glass rectifiers are usually made into units capable of D.C. output (maximum continuous rating) of
200 A at 200 V
300 A at 300 V
400 A at 400 V
500 A at 500 V
ANSWER : : 500 A at 500 V
17.Which of the following metals is generally manufactured by electrolysis process ?
Load
Aluminium
Copper
Zinc
ANSWER : : Aluminium
18.The cathdde voltage drop, in a mercury arc rectifier, is due to
expenditure of energy in ionization
surface resistance
expenditure of energy in overcoming the electrostatic field
expenditure of energy in liberating electrons from the mercury
ANSWER : : expenditure of energy in liberating electrons from the mercury
19.A rotary converter in general construction and design, is more or less like
a transformer
an induction motor
an alternator
any D.C. machine
ANSWER : : any D.C. machine
20.A rotary converter combines the function of
an induction motor and a D.C. generator
a synchronous motor and a D.C. generator.
a D.C. series motor and a D.C. generator
none of the above
ANSWER : : a synchronous motor and a D.C. generator.
21.The voltage drop between the anode and cathode, of a mercury arc rectifier comprises of the following
anode drop and cathode drop
anode drop and arc drop
cathode drop and arc drop
anode drop, cathode drop and arc drop
ANSWER : s: d
22.A rotary converter is a single machine with
one armature and one field
two armatures and one field
one armature and two fields
none of the above
ANSWER : : one armature and one field
23.The ionization potential of mercury is approximately
5.4 V
8.4 V
10.4 V
16.4 V
ANSWER : : 10.4 V
24.A synchronous converter can be started
by means of a small auxiliary motor
from AC. side as induction motor
from D.C. side as D.C. motor
any of the above methods
ANSWER : : any of the above methods
25.Which of the following rectifiers are primarily used for charging of low voltage batteries from AC. supply ?
Mechanical rectifiers
Copper oxide rectifiers
Selenium rectifiers
Electrolytic rectifiers
ANSWER : : Electrolytic rectifiers
26.The efficiency of the copper oxide rectifier seldom exceeds
90 to 95%
85 to 90%
80 to 85%
65 to 75%
ANSWER : : 65 to 75%
27.The metal rectifiers, as compared to mercury arc rectifiers
operate on low temperatures
can operate on high voltages
can operate on heavy loads
give poor regulation
ANSWER : : operate on low temperatures
28.When a rectifier is loaded which of the following voltage drops take place ?
Voltage drop in transformer reactance
Voltage drop in resistance of transformer and smoothing chokes
Arc voltage drop
All of the above
ANSWER : : All of the above
29.In a glass bulb mercury arc rectifier the maximum current rating is restricted to
2000 A
1500 A
1000 A
500 A
ANSWER : : 500 A
30.In a mercury arc rectifier______ flow from anode to cathode
ions
electrons
ions and electrons
any of the above
ANSWER : : ions
31.In a mercury arc rectifier characteristic blue luminosity is due to
colour of mercury
ionization
high temperature
electron streams
ANSWER : : ionization
32.The metal rectifiers are preferred to valve rectifiers due to which of the following advantages ?
They are mechanically strong
They do not require any voltage for filament heating
Both (a) and (b)
None of the above
ANSWER : : Both (a) and (b)
33.Which of the following rectifiers have been used extensively in supplying direct current for electroplating ?
Copper oxide rectifiers
Selenium rectifiers
Mercury arc rectifiers
Mechanical rectifiers
ANSWER : : Selenium rectifiers
34.Ageing of a selenium rectifier may change the output voltage by
5 to 10 per cent
15 to 20 per cent
25 to 30 per cent
none of the above
ANSWER : : 5 to 10 per cent
35.Which of the following statement is incorrect ?
Copper oxide rectifier is a linear device
Copper oxide rectifier is not a perfect rectifier
Copper oxide rectifier has a low efficiency
Copper oxide rectifier finds use in control circuits
ANSWER : : Copper oxide rectifier is a linear device
36.Which of the following mercury arc rectifier will deliver least undulating current?
Six-phase
Three-phase
Two-phase
Single-phase
ANSWER : : Six-phase
37.A commutating rectifier consists of commutator driven by
an induction motor
a synchronous motor
a D.C. series motor
a D.C. shunt motor
ANSWER : : a synchronous motor
38.In mercury arc rectifiers having grid, the arc can be struck between anode and cathode only when the grid attains a certain potential, this potential being known as
maximum grid voltage
critical grid voltage
any of the above
none of the above
ANSWER : : critical grid voltage
39.A mercury arc rectifier possesses ________ regulation characteristics
straight line
curved line
exponential
none of the above
ANSWER : : none of the above
40.Selenium rectifier can be operated at temperatures as high as
25�C
40�C
60�C
75�C
ANSWER : : 75�C
41.It is the_______of the transformer on which the magnitude of angle of overlap depends.
resistance
capacitance
leakage reactance
any of the above
ANSWER : : leakage reactance
42.In a grid control of mercury arc rectifiers when the grid is made positive relative to cathode, then it the electrons on their may to anode.
accelerates
decelerates
any of the above
none of the above
ANSWER : : accelerates
43.The applications of selenium rectifiers are usually limited to potential of
10 V
30 V
60 V
100 V
ANSWER : : 100 V
44.The ignited or auxiliary anode in mercury arc rectifier is made of
graphite
boron carbide
aluminum
copper
ANSWER : : boron carbide