# 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]) 42.4sin50Ï€t.**

B [ ]) 30sin50Ï€t.

C [ ]) 30sin25Ï€t.

D [ ]) 42.4sin25Ï€t.

**E [ ]) HINTS-**ImsinÏ‰t = Imsin2Ï€ft.,Im = √2 X 30 = 42.4 A ,f is here 25 Hz ,equation will be

42.4sin2Ï€25t = 42.4sin50Ï€t.

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 Î© and R2 = 75 Î©, each having tolerance of ±5% are connected in series. The

value of resultant resistance is

A [ ]) 111 ± 0 Î©.

B [ ]) 111 ± 2.77 Î©.

**C [v]) 111 ± 5.55 Î©.**

D [ ]) 111 ± 7.23 Î©

**E [ ]) HINTS-**R1 = 36 ± 5% = 36 ± 1.8 Î©. R2 = 75 ± 5 % =75 ± 3.75 Î©. ∴ R1 + R2 = 111 ± 5.55

Î©.

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 cosÏ†=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=2Î© 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=2Î© 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+1**D [ ]) 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 sinÏ† = reactive power , Active power = 1200 W , cosÏ† = 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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