WIREMAN S3

WIREMAN THEORY

SEM 3 JAN 2018

One that is based on forward biased PN junction is .......
a) Photo diode
c) Photo voltaic cell
b) LED
d) Both (a) and (b)

Which of these is a best description of a zener diode?
a) It operates in the reverse region
b) It is a constant voltage device
c) It is a constant current device
d) None of these

The LED is usually made of material like-
a) GaAs
b) C and Sl
c) GeAs
d) None of these

Zener diode are used as-
a) Reference voltage element
b) Reference current element
c) Reference resistance
d) None of these

Zener diode are
a) Specially doped p -- n junction
b) Normally doped p — n junction
c) Lightly doped p—n junction
d) None of these

ICs are generally made of
a) Silicon
b) Germanium
c) Copper
d) Nonc of these

The active components in an IC are
a) Resistors
b) Capacitors
c) Transistors and diodes
d) None of these

Diode characteristic curve is a plot between-
a) Current and time
b) Voltage and time
c) Voltage and current
d) Both (a) & (b)

In case a PN junction is biased-
a) Hole and electrons seize to move
b) Electrons and holes mov towards the junction
c) Electrons and holes move away from the junction
d) Depletion region decreases

The element that has the biggest size in a transistor is
a) Collector
c) Emitter
b) Base
d) Collector-base-junction

The value of a of a transistor is
a) More than 1
b) Less than 1
c) 1
d) None of these

The voltage gain in a transistor connected in   arrangement is the highest.
a) Common base
c) Common emitter
b) Common collector
d) None of these

A SCR is  switch.
a) One directional
c) Three directional
b) Two directional
d) Four directional

A silicon controlled rectifier (SCR) is a-
a) Unijunction device
b) Device with four junctions
c) Device with three junctions
d) None of these

Which of the following finds applications in speed control of D.C. motor?
a) FET
b) SCR
c) NPN transistor
d) None of these

A UJT has
a) Two pn junction
b) Three pn junction
c) One pn junction
d) None of these

The fuse rating is expressed in terms of-
a) Current
b) VAR
c) Voltage
d) KVA

MCCB are commonly used for operating current between-
a) 63 amps. To 800 amps
b) 16 amps. To 32 amps
c) 5 amps. To 16 amps
d) None of these

ELCB is an abbreviation for*
a) Electrolytic circuit breaker
b) Earth leakage circuit breaker
c) Earth locking circuit breaker
d) Electric leakage circuit breaker

Miniature circuit breaker is a small-
a) Fuse
b) Electromagnetic switch
c) Magnetic switch
d) Two way switch

For soldering of platinum, tungsten, steel etc. the solder used is-
a) Cabmium-solder
b) Tin - lead - silver solder
c) Tin lead solder
d) Copper silver - zinc solder

The following magnet is used in large machines to create magnetic flux-
a) Permanent magnet
b) Temporary magnet
c) Electro magnet
d) Any of these

Function ofis to collect Current from the commutator and supply it to the external  load.
a) Field magnet
b) Brushes
c) Armature
d) Yoke

Which of the following generators have two field windings?
a) Series wound generator
b) Compound wound generator
c) Shunt wound generator
d) All of these

In a separately excited D.C generator the field is connected to-
a) In series with an armature
b) To the external supply source
c) Across the armature
d) None of these

The annature reaction in D.C machine causes distortion in the main field flux. This effect of   armature reaction can be reduced by-
a) Increasing the length of air gap
b) Increasing the number of poles
c) Decreasing the length of air gap
d) Decreasing the nurnber of poles

In a dc generator the polarity of interpole is-
a) Always N
b) Always S
c) Same as the polarity of the main pole that follows in the direction of rotation
d) Same as the polarity of the

main pole that proceeds in the direction of rotation

The function of the commutator in a D.C machine is-
a) To change ac to dc
b) To change altemating voltage to direct voltage
c) For easy control of voltage
d) None of the above

Winding generator will have-
a) Wave wound
b) Delta wound
c) Lap wound
d) Duplex wound

lhe efficiency of a D.C shunt generator has a maximum value when-
a) Magnetic losses are equal to mechanical losses
b) Armature copper loss is equal to the constant loss
c) Field copper loss is equal to the constant loss.
d) None of the above

For parallel operation the generators normally preferred are-
a) Series generator
b) Compound generator
c) Shunt generator
d) Series and shunt generator

Interpoles in the armature of a D.C generator are used toe
a) Neutralize the reactance voltage
b) Neufralize the reactance voltage and the cross-magnetizing effect of the armature reaction
c) Neutralize the cross-magnetizing effect of the armature reaction
d) None of the above

Which DC motor has approximately constant speed?
a) Series
b) Cumulatively compound motor
c) Shunt
d) All of these

A series motor-
a) Should always be started on load
b) Always runs at constant speed
c) Is not suitable for high starting torque
d) May 'run away' if the field gets opened

The back emf of a DC rnotor depend on-
a) Field flux
b) Type of slip rings
c) Shape of conductors d) Brush material

The electromagnetic torque and speed are in the same direction in case
a) DC motors
b) DC generators
c) Both DC motors as well as DC generators
d) None of the above

In DC motor, the conditions for maximum power is-
a) Supply voltage = h x back e.m.f.
b) Supply voltage = 4x back e.m.f.
c) Supply voltage = 2 x supply voltage
d) Supply voltage = h x supply voltage

The speed of a DC motor is-
a) Always constant
b) Directly proportional to back e.m.f.
c) Directly proportional to flux
d) Directly proportional to the product cfback e.m.f. and flux

The direction of rotation of a compound dc motor can be effectively reversed by interchanging-
a) Shunt field connections
b) Armature connection
c) Series field connections
d) Line leads

Two wattmeter connected to measure the power in a balanced 3 phase load will indicate same reading when load p.f. is -
a) Zero
b) Unity
c) 0.5
d) None of these

In a 3 phase, 4 wire star-connected system the voltage across the phases is ..volts.
a) 400
c) 500
b) 200
d) None of these

In a balance 3-phase load, the current in the neutral will be
a) 0    b) 1    c) 2    d) 5

The rating of Alternator / Generator may be expressed in ...............
a) KW
c) KVAR
b) kva
d) HP

Single phase motor generally used for small air compressor is .....
a) Capacitor start and capacitor lun motor
b) Universal motor
c) Reluctance motor
d) Shaded pole motor

A capacitor start, capacitor run single phase induction motor is basically a-
a) AC series motor
b) 3 Phase induction motor
c) 2 Phase induction motor
d) DC series motor

A three phase slip ring induction motor has-
a) Short Circuited rotor
b) Wound rotor
c) Double cage rotor
d) All of these

Switch not used in the house wiring circuit is -
a) Single way switch
b) Two way switch
c) Push button switch
d) Knife switch

The direction of rotation of 3 phase induction motor can be reversed by-
a) Reducing load
c) Supplying low voltage
b) Reducing frequency
d) Interchanging any two phases

Slip ring induction motors are employed only for-
a) Speed control
c) Both (a) and (b)
b) High starting torque
d) None of these

For induction motors-
a) Should be essentially a constant speed motor
b) Its speed reduces to some extent with increase in load
c) Does not need to be synchronized
d) All of the above