1. Which of the following are the applications of D.C. system ?
(a) Battery charging work
(b) Arc welding
(c) Electrolytic and electro-chemical processes
(d) Arc lamps for search lights
(e) All of the above
Ans: e
2. Which of the following methods may be used to convert A.C. system to D.C. ?
(a) Rectifiers
(b) Motor converters
(c) Motor-generator sets
(d) Rotary converters
(e) All of the above
Ans: e
3. In a single phase rotary converter the number of slip rings will be
(a) two
(b) three
(c) four
(d) six
(e) none
Ans: a
4. A synchronous converter can be started
(a) by means of a small auxiliary motor
(b) from AC. side as induction motor
(c) from D.C. side as D.C. motor
(d) any of the above methods
(e) none of the above methods
Ans: d
5. A rotary converter is a single machine with
(a) one armature and one field
(b) two armatures and one field
(c) one armature and two fields
(d) none of the above
Ans: a
6. A rotary converter combines the function of
(a) an induction motor and a D.C. generator
(b) a synchronous motor and a D.C. generator.
(c) a D.C. series motor and a D.C. generator
(d) none of the above
Ans: b
7. Which of the following is reversible in action ?
(a) Motor generator set
(b) Motor converter
(c) Rotary converter
(d) Any of the above
(e) None of the above
Ans: c
8. Which of the following metals is generally manufactured by electrolysis process ?
(a) Load
(b) Aluminium
(c) Copper
(d) Zinc
(e) None of the above
Ans: b
9. With a motor converter it is possible to obtain D.C. voltage only upto
(a) 200-100 V
(6) 600—800 V
(c) 1000—1200 V
(d) 1700—2000 V
Ans: d
10. Normally, which of the following is used, when a large-scale conversion from AC. to D.C. power is required ?
(a) Motor-generator set
(b) Motor converter
(c) Rotary converter
(d) Mercury arc rectifier
Ans: d
11. A rotary converter in general construction and design, is more or less like
(a) a transformer
(b) an induction motor
(c) an alternator
(d) any D.C. machine
Ans: d
12. A rotary converter operates at a
(a) low power factor
(6) high power factor
(c) zero power factor
(d) none of the above
Ans: b
13. In which of the following applications, direct current is absolutely essential ?
(a) Illumination
(b) Electrolysis
(c) Variable speed operation
(d) Traction
Ans: b
14. Which of the following AC. motors is usually used in large motor-generator sets?
(a) Synchronous motor
(b) Squirrel cage induction motor
(c) Slip ring induction motor
(d) Any of the above
Ans: a
15. In a rotary converter armature currents are
(a) d.c. only
(b) a.c. only
(c) partly a.c. and partly d.c.
Ans: c
16. In which of the following equipment direct current is needed ?
(a) Telephones
(b) Relays
(c) Time switches
(d) All of the above
Ans: d
17. In a rotary converter I2R losses as compared to a D.C. generator of the same size will be
(a) same
(b) less
(c) double
(d) three times
Ans: b
18. In a mercury arc rectifier positive ions are attracted towards
(a) anode
(b) cathode
(c) shell bottom
(d) mercury pool
Ans: b
19. Mercury, in arc rectifiers, is chosen for cathode because
(a) its ionization potential is relatively low
(b) its atomic weight is quite high
(c) its boiling point and specific heat are low
(d) it remains in liquid state at ordi¬nary temperature
(e) all of the above
Ans: e
20. The ionization potential of mercury is approximately
(a) 5.4 V
(b) 8.4 V
(c) 10.4 V
(d) 16.4 V
Ans: c
21. The potential drop in the arc, in a mercury arc rectifier, varies
(a) 0.05 V to 0.2 V per cm length of the arc
(b) 0.5 V to 1.5 V per cm length of the arc
(c) 2 V to 3.5 V per cm length of the arc
(d) none of the above
Ans: d
22. The voltage drop between the anode and cathode, of a mercury arc rectifier comprises of the following
(a) anode drop and cathode drop
(b) anode drop and arc drop
(c) cathode drop and arc drop
(d) anode drop, cathode drop and arc drop
Ans: d
23. Glass rectifiers are usually made into units capable of D.C. output (maximum continuous rating) of
(a) 100 A at 100 V
(b) 200 A at 200 V
(c) 300 A at 300 V
(d) 400 A at 400 V
(e) 500 A at 500 V
Ans: e
24. The voltage drop at anode, in a mercury arc rectifier is due to
(a) self restoring property of mercury
(b) high ionization potential
(c) energy spent in overcoming the electrostatic field
(d) high temperature inside the rectifier
Ans: c
25. The internal efficiency of a mercury arc rectifier depends on
(a) voltage only
(b) current only
(c) voltage and current
(d) r.m.s. value of current
(e) none of the above
Ans: a
26. If cathode and anode connections in a mercury arc rectifier are inter changed
(a) the rectifier will not operate
(b) internal losses will be reduced
(c) both ion and electron streams will move in the same direction
(d) the rectifier will operate at reduced efficiency
Ans: a
27. The cathdde voltage drop, in a mercury arc rectifier, is due to
(a) expenditure of energy in ionization
(b) surface resistance
(c) expenditure of energy in overcoming the electrostatic field
(d) expenditure of energy in liberating electrons from the mercury
Ans: d
28. To produce cathode spot in a mercury arc rectifier
(a) anode is heated
(b) tube is evacuated
(c) an auxiliary electrode is used
(d) low mercury vapour pressures are used
Ans: c
29. The advantage of mercury arc rectifier is that
(a) it is light in weight and occupies small floor space
(b) it has high efficiency
(c) it has high overload capacity
(d) it is comparatively noiseless
(e) all of the above
Ans: e
30. In a mercury pool rectifier, the voltage drop across its electrodes
(a) is directly proportional to load
(b) is inversely proportional to load
(c) varies exponentially with the load current
(d) is almost independent of load current
Ans: d