SSC/ UPPCL JE Electrical Important
MCQ Part 12
1.Lenz’s Law follows from
A. Principle of conservation of mass
B. Principle of superposition
C. Principle of conservation of
energy
D. Principle of homogeneity
Answer : C
2.The coupling coefficient for the
transformer below
A. 0
B. 1
C. 0.56
D. 0.98
Answer : C
(k=M/√L₁L₂=2.5/√5*4=0.56)
3.An ideal transformer, connected to
a 240 V mains, supplies power to a 12 V, 150 W lamp.The current drawn from the
mains is
A. 0
B. 1
C. 0.05
D. 0.625
Answer : D
(Secondary current
I₂=P/V₂=150/12=12.5 A
The transformation ratio n=V₂/V₁=12/240=0.05
The current drawn from supply I₁=I₂×n=12.5×0.05=0.625 A)
The transformation ratio n=V₂/V₁=12/240=0.05
The current drawn from supply I₁=I₂×n=12.5×0.05=0.625 A)
4.The dependent source in Fig is
(a) Voltage-controlled current source
(b) Voltage-controlled voltage
source
(c) Current-controlled voltage
source
(d) Current-controlled current
source
Answer : D (A current source
that depends on a current input is generally referred to as a Current
Controlled Current Source or CCCS)
5.The current iₒ and voltage vₒ in
the circuit shown in Fig is
A. 6 A,24 V
B. 3 A,12 V
C. 4 A,8 V
D. 2 A,4 V
Answer : A
(Applying KCL to node a, we obtain
3 + 0.5 iₒ = iₒ ⇒ iₒ = 6 A
For the 4-Ω resistor, Ohm’s law gives
vₒ= 4 iₒ = 24 V)
3 + 0.5 iₒ = iₒ ⇒ iₒ = 6 A
For the 4-Ω resistor, Ohm’s law gives
vₒ= 4 iₒ = 24 V)
6.What is the form factor of pure
sine wave
A. 1.11
A. 1.11
B. 1.414
C. 1.57
D. 0.909
Answer : A (Form
Factor is the ratio between the average value and the RMS value and is
given as. For a pure sinusoidal waveform the Form Factor will
always be equal to 1.11)
7. A network with b branches, n nodes,
and l independent loops will satisfy which of the
A. b=l-n+1
B. b= n-l+1
C.b=l+n-1
D. b=l-n-1
Answer : C
8.Total losses occurring in a
transformer when it is operating at its maximum efficiency are 2000 W. The
total copper losses is
A. 2000 W
B. 1000 W
C. 1500 W
D. 800 W
Answer : B
(The condition for maximum
efficiency is, Full load copper loss Pc = Iron loss, Pi
,Total loss P = Pc + Pi = 1000 + 1000 = 2000 W)
9.A salient pole machine is used for
A. Low speed applications in Hydro
plants
B. High speed applications in Hydro
plants
C. Low speed applications in Thermal
plants
D. High speed applications in
Answer : A
10.If a three-phase, 8–pole, 50 Hz
induction motor runs at a speed of 735 r.p.m. then the slip is
A. 0.02
B. 0.03
C. 0.04
D. 0.05
Answer : A
(Ns=120*f/P=120*50/8=750,s=(Ns-Nr)/Ns=(750-735)/750=15/750=0.02)
11.In an oil- filled transformer,
oil is provided for
A. Cooling
B. Insulation
C. Lubrication
D.Both Cooling and insulation
Answer : D
12.Kirchoff’s Laws are applicable
for
A. DC circuits only
B. Circuits with rectified AC supply
C. Both AC and DC circuits
D.AC circuits only
Answer : C
13.In a Y-Y system, a line voltage
of 220 V produces a phase voltage of
A. 381 V
B. 311 V
C. 220 V
D. 127 V
Answer : D
(Vph=VL/√3=220/√3=127.02 V)
14.A commutator in a DC machine can
convert
A. AC to DC
B. DC to AC
C. Pulsating to DC
D. Both AC to DC & DC to AC
Answer : D (In DC Generator
the commutator converts AC to DC,In DC Motor DC to AC ,Thus Commutator in a DC
machine converts both AC to DC and DC to AC)
15.The main purpose of using a core
in transformer is to
A. Decrease iron loss
B. Prevent eddy current loss
C. Eliminate magnetic hysteresis
D. Decrease reluctance of the
magnetic circuit
Answer : D
16.In a particular meter, the
operating torque is directly proportional to the current passing through it ,
then the type of meter is
A. moving iron
B. moving coil
C. electrostatic
D. induction
Answer : B
17.Short circuit test on transformer
is conducted to obtain
A. Core losses at any load
B. Hysteresis loss only
C. Ohmic Loss
D. Eddy Current Loss only
Answer : C
18.Out of the following which
machine is also known as a generalized transformer
A. DC motor
B. Induction Motor
C. DC generator
D. Synchronous motor
Answer : B
19.The rating of a transformer is
expressed in
A. KVA
B. KW
C. HP
D. W
Answer : A
20.If the current through a 10-mH
inductor increases from zero to 2 A, how much energy is stored in the inductor
A. 40 mJ
B. 20 mJ
C. 10 mJ
D. 5 mJ
Answer : B (Energy is stored
in the inductor=LI²/2=10×2²/2=20 mJ)
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