ELECTRICAL ENGINEERING IMPORTANT MCQ-BASIC ELECTRICAL PART THREE


ANSWER KEY-Correct
answer is indicated by symbol (V) in options.

HINTS-In some questions options
E-HINTS is indicating the hints of answer.

1) The equation for 25 cycles current sine wave having rms value of 30 amps, will be
A [v]) 42.4sin50πt.
B [ ]) 30sin50πt.
C [ ]) 30sin25πt.
D [ ]) 42.4sin25πt.
E [ ]) HINTS-Imsinωt = Imsin2πft.,Im = √2 X 30 = 42.4 A ,f is here 25 Hz ,equation will be
42.4sin2π25t = 42.4sin50πt.

2) The internal resistance of a practical voltage source is considered to be connected in
A [v]) series.
B [ ]) parallel.
C [ ]) either parallel or series.
D [ ]) none of the above.

3) R1 = 36 Ω and R2 = 75 Ω, each having tolerance of ±5% are connected in series. The
value of resultant resistance is
A [ ]) 111 ± 0 Ω.
B [ ]) 111 ± 2.77 Ω.
C [v]) 111 ± 5.55 Ω.
D [ ]) 111 ± 7.23 Ω
E [ ]) HINTS-R1 = 36 ± 5% = 36 ± 1.8 Ω. R2 = 75 ± 5 % =75 ± 3.75 Ω. ∴ R1 + R2 = 111 ± 5.55
Ω.

4) The form factor of sinusoidal alternating current is
A [ ]) 0.
B [ ]) 1
C [v]) 1.11
D [ ]) 1.15
E [ ]) HINTS-form factor=rms value /average value=0.707/0.637=1.11

5) Whenever current is supplied by a source its terminal voltage
A [ ]) increases.
B [v]) decreases.
C [ ]) remains constant.
D [ ]) increases exponentially.

6) A current of 4 A flows in an AC circuit when 100 V DC is applied to it whereas it takes
250 V AC to produce the same current the power factor of the circuit is
A [v]) 0.4.
B [ ]) 10.
C [ ]) 1.
D [ ]) 0.85.
E [ ]) HINTS=FOR DC,R=V/I=100/4=25 Ohm
FOR AC,Z=V/I=250/4=62.5 Ohm
power factor cosφ=R/Z=25/62.5=0.4

7) A branch of a network is said to be active when it consists of one
A [ ]) resistor.
B [v]) voltage source .
C [ ]) inductor.
D [ ]) capacitor

8) A branch of a network is said to be passive when it contains
A [v]) voltmeter.
B [ ]) voltage source.
C [ ]) current source
D [ ]) battery.

9) terminal voltage is equal to the source emf.
A [ ]) terminal voltage can not exceed source emf.
B [v]) terminal voltage is always lower than source emf.
C [ ]) terminal voltage is higher than the source emf.
D [ ]) terminal voltage is equal to the source emf.

10) To neglect a voltage source, the terminals across the source are
A [ ]) open circuited.
B [ V]) short circuited.
C [ ]) replaced by some resistance.
D [ ]) replaced by inductor.

11) A network consists of linear resistors and ideal voltage source. If the value of resistors
are doubled, then voltage across each resistor is
A [ ]) halved.
B [ ]) doubled.
C [ ]) increased four lines.
D [v]) not changed.

12) A practical current source is represented by
A [ ]) a resistance in series with an ideal current source.
B [v]) a resistance in parallel with an ideal current source.
C [ ]) a resistance in parallel with an ideal voltage source.
D [ ]) none of above.

13) Constant voltage source is
A [ ]) active and bilateral.
B [ ]) passive and bilateral.
C [v]) active and unilateral.
D [ ]) passive and unilateral.

14) Total power consumed in the circuit below is 10 W. Find x.

A [ ]) 1 A.
B [v]) 2 A.
C [ ]) 3 A.
D [ ]) None of these.
E [ ]) HINTS-Total power consumed = x² X 2 + 2²/2 ∴ 10 W = 2x² + 2 Therefore, x = 2 A.

15) In which braking back emf exceeds supply voltage?
A [v]) Regenerative.
B [ ]) Dynamic.
C [ ]) Plugging.
D [ ]) None of these.

16) Our household apparatus are connected in
A [v]) parallel.
B [ ]) series.
C [ ]) cascade.
D [ ]) series and parallel combination.

17) In a delta network each element has value R. The value of each element in equivalent
star network will be
A [ ]) R / 6
B [ ]) R / 4.
C [ ]) R / 2.
D [v]) R / 3.

18) Nodal analysis can be applied for
A [ ]) planar networks.
B [ ]) non planar networks.
C [v]) both planner and non planner networks.
D [ ]) neither planner nor non planner networks.

19) Mesh analysis is applicable for
A [v]) planar networks
B [ ]) non planarnetworks
C [ ]) both planner and non planner networks.
D [ ]) neither planner nor non planner networks.

 20) KCL works on the principle of which of the following
A [v]) Law of conservation of charge
B [ ]) Law of conservation of energy
C [ ]) both
D [ ]) None of these

21) KVL works on the principle of
A [ ]) Law of conservation of charge
B [v]) Law of conservation of energy
C [ ]) Both
D [ ]) none of these

22) Super mesh analysis is used in case of
A [ ]) Ideal voltage source is connected between two non reference nodes
B [v]) Current source branch is common for two meshes
C [ ]) Both
D [ ]) Either 1 or 2

23) When we use super node technique
A [ ]) Current source branch is common for two meshes
B [v]) Ideal voltage source is connected between two non reference nodes
C [ ]) Both
D [ ])All of the above

24) If a resistor is connected across the voltage source and the frequency of voltage and
current wave form is 50Hz, then what is frequency of instantaneous power
A [ ]) 0 Hz
B [v]) 100Hz
C [ ]) 50Hz
D [ ]) 150Hz

25) In a series R, L circuit, voltage across resistor and inductor are 3 V and 4 V
respectively, then what is the applied voltage
 A [ ]) 7V
B [v]) 5V
C [ ]) 4V
D [ ]) 3V

26) The alternative names for active power is/are
A [ ]) Real power
B [ ]) Average power
C [ ]) True power
D [v]) All of the above

27) In series R, L circuit power factor can be defined as
A [ ]) R/Z
B [ ]) P/S
C [ ]) Vr/V
D [v]) All of the above

28) In RLC series circuit, if the voltage across capacitor is greater than voltage across
inductor, then power factor of the network is
A [ ]) lagging
B [v]) leading
C [ ]) unity
D [ ]) zero

29) In RLC parallel circuit circuit current through inductor is more than current through
capacitor. Then what is the power factor of the circuit?
A [v]) lagging
B [ ]) leading
C [ ]) unity
D [ ]) zero

30) When power factor angle is varying, the shape of the current locus is
 A [v]) Semi circle
B [ ]) Circle
C [ ]) Triangle
D [ ]) Straight line

31) In RLC parallel circuit if current through capacitor and inductor is equal. Then What is
the power factor?
A [ ]) lagging
B [ ]) leading
C [v]) unity
D [ ]) zero

32) By which of the following elements transients will not occur?
A [v]) R
B [ ]) L
C [ ]) C
D [ ]) All of the above

33) For steady state current inductor acts as
A [v]) Short circuit
B [ ]) Open circuit
C [ ]) Voltage source
D [ ]) Current source

34) In RL series circuit R=2Ω and L=10mH and applied voltage is 10V DC. Then find the
current in the network?
A [ ]) 0A
B [ ]) 10A
C [v]) 5A
D [ ]) 1A
E [ ]) HINTS-For DC voltage inductor acts as a short circuit at steady state. I=V/R=10/2=5

35) In steady state condition capacitor acts as a
A [ ]) Short circuit
B [v]) Open circuit
C [ ]) Voltage source
D [ ]) Current source

36) Time constant of RL series circuit is
A [ ]) 2L/R
B [ ]) RC
C [v]) L/R
D [ ]) 2RC

37) Time constant of RC series circuit is
A [ ]) L/R
B [ ]) 2RC
C [ ]) 2L/R
D [v]) RC

38) In RL series circuit R=2Ω and L=2mH. What is the value of time constant?
A [v]) 1msec
B [ ]) 2msec
C [ ]) 4msec
D [ ]) 100sec

39) Time constant is the time taken for response to rise ——-of maximum value?
A [ ]) 100%
B [ ]) 90%
C [v]) 63.2%
D [ ]) 68.3%

40) Image impedance can be written by using short circuit impedance(Zsc)and open circuit
impedance(Zoc) as
A [ ]) Zsc+Zoc
B [ ]) Zsc-Zoc
C [ ]) Zsc/Zoc
D [v]) (Zsc . Zoc)½

41) Given network is having N nodes and B branches, then number of twigs are
A [ ]) N
B [v]) N-1
C [ ]) B-N+1
D [ ]) B-N-1

42) Given network is having N nodes and b branches, then number of individual loops are
A [ ]) N
B [ ]) N-1
C [v]) b-N+1D [ ]) b-N-1

43) Mesh analysis is preferred when loops are——nodes
A [v]) less than
B [ ]) greater than
C [ ]) equals to
D [ ]) any of the above

44) A motor having a power factor of 0.8 absorbs in active power of 1200 W the reactive
power drawn from the supply is _________ VA.
A [ ]) 130.
B [v]) 900.
C [ ]) 250.
D [ ]) 400.
E [ ]) HINTS- VI sinφ = reactive power , Active power = 1200 W , cosφ = 0.8 VI = 1200 / 0.8,
reactive power = 1200 / 0.8 × 0.6 = 900 VA.

45) the coils having self inductor of 10 mH and 15 mH have an effective inductor of 40 mH ,
when connected in series aiding. What will be the equivalent inductor if we connect them in
series opposing
A [ ]) 20 mH.B [ ]) 5 mH.
C [ ]) 0 mH.
D [v]) 10 mH
E [ ]) HINTS- L = L1 + L2 + 2M, when ordinary 40 = 10 + 15 + 2M 2M = 15 mH L = L1 + L2 – 2M ,
when opposing L = 10 mH

46) Reactive power drawn by a pure resistor is
A [v]) 0
B [ ]) minimum
C [ ]) maximum
D [ ]) none of the above

47) Kirchhoffs laws are valid for
A [v]) linear circuit only.
B [ ]) passive time invariant circuits.
C [ ]) non-linear circuits only.
D [ ]) both linear and non-linear circuits.

48) In what connection we get neutral?
A [v]) Star.
B [ ]) Delta.
C [ ]) Mesh.
D [ ]) Both A and B.

49) What is the relation between line voltage and phase voltage in case of delta
connection?
A [v]) VL = VP.
B [ ]) VL =1/ VP.
C [ ]) VL = √3VP.
D [ ]) ALL OF THESE

50) If a resistor and an inductor are connected in series across a voltage source. Which
two parameters in that circuit increase if frequency of voltage source increases?
A [v]) VL and Z.
B [ ]) Z and I.
C [ ]) VL and I.
D [ ]) VL and VR.
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