AC Fundamentals, Circuits & Circuit Theory Mcqs - Set 5

1)   Aphasoris________?

a. a line which represents the magnitude and phase of an alternating quantity
b. a line representing the magnitude and direction of an alternating quantity
c. a coloured tag or band for distinction between different phases of a 3-phase supply
d. an instrument used for measuring phases of an unbalanced 3-phase load
Answer  Explanation 

ANSWER: a line which represents the magnitude and phase of an alternating quantity

Explanation:
No explanation is available for this question!


2)   Which of the following statements pertains to resistors only _____________?

a. can dissipate considerable amount of power
b. can act as energy storage devices
c. connecting them in parallel in¬creases the total value
d. oppose sudden changes in voltage
Answer  Explanation 

ANSWER: can dissipate considerable amount of power

Explanation:
No explanation is available for this question!


3)   Wire-wound resistors are unsuitable for use at high frequencies because they_______?

a. create more electrical noise
b. are likely to melt under excessive eddy current heat
c. consume more power
d. exhibit unwanted inductive and capacitive effects
Answer  Explanation 

ANSWER: exhibit unwanted inductive and capacitive effects

Explanation:
No explanation is available for this question!


4)   The purpose of a parallel circuit resonance is to magnify________?

a. current
b. voltage
c. power
d. frequency
Answer  Explanation 

ANSWER: voltage

Explanation:
No explanation is available for this question!


5)   All definitions of power factor of a series R-L-C circuit are correct except__________?

a. ratio of net reactance and impedance
b. ratio of kW and kVA
c. ratio of J and Z
d. ratio of W and VA
Answer  Explanation 

ANSWER: ratio of net reactance and impedance

Explanation:
No explanation is available for this question!


6)   In AC. circuits, laminated iron is invariably used in order to__________?

a. reduce eddy current loss
b. increase heat radiation
c. make assembly cheap and easier
d. reduce circuit permeability
Answer  Explanation 

ANSWER: reduce eddy current loss

Explanation:
No explanation is available for this question!


7)   A parallel AC. circuit in resonance will__________?

a. have a high voltage developed across each inductive and capacitive section
b. have a high impedance
c. act like a resistor of low value
d. have current in each section equal to the line current
Answer  Explanation 

ANSWER: have a high impedance

Explanation:
No explanation is available for this question!


8)   The apparent power drawn by an A.C. circuit is 10 kVA and active power is 8 kW. The reactive power in the circuit is_________?

a. 4 kVAR
b. 6 kVAR
c. 8 kVAR
d. 16 kVAR
Answer  Explanation 

ANSWER: 6 kVAR

Explanation:
No explanation is available for this question!


9)   The ratio of active power to apparent power is known as factor__________?

a. demand
b. load
c. power
d. form
Answer  Explanation 

ANSWER: power

Explanation:
No explanation is available for this question!


10)   The effective resistance of an iron-cored choke working on ordinary supply frequency is more than its true resistance because of____________?

a. iron loss in core
b. skin effect
c. increase in temperature
d. capacitive effect between adjacent coil turns
Answer  Explanation 

ANSWER: iron loss in core

Explanation:
No explanation is available for this question!


11)   A pure inductance connected across 250 V, 50 Hz supply consumes 100 W. This consumption can be attributed to_________?

a. the big size of the inductor
b. the reactance of the inductor
c. the current flowing in the inductor
d. the statement given is false
Answer  Explanation 

ANSWER: the statement given is false

Explanation:
No explanation is available for this question!


12)   The input of an A.C. circuit having power factor of 0.8 lagging is 40 kVA The power drawn by the circuit is__________?

a. 12 kW
b. 22 kW
c. 32 kW
d. 64 kW
Answer  Explanation 

ANSWER: 32 kW

Explanation:
No explanation is available for this question!


13)   In an AC. circuit, a low value of kVAR compared with kW indicates_________?

a. low efficiency
b. high power factor
c. unity power factor
d. maximum load current
Answer  Explanation 

ANSWER: high power factor

Explanation:
No explanation is available for this question!


14)   Which of the following coil will have large resonant frequency __________?

a. A coil with large resistance
b. A coil with low resistance
c. A coil with large distributed capacitance
d. A coil with low distributed capacitance
Answer  Explanation 

ANSWER: A coil with large distributed capacitance

Explanation:
No explanation is available for this question!


15)   If a sinusoidal wave has frequency of 50 Hz with 30 A r.m.s. current which of the following equation represents this wave_________ ?

a. 42.42 sin 3141
b. 60 sin 25 t
c. 30 sin 50 t
d. 84.84 sin 25 t
Answer  Explanation 

ANSWER: 42.42 sin 3141

Explanation:
No explanation is available for this question!


16)   In a R-L-C circuit_________?

a. power is consumed in resistance and is equal to I R
b. exchange of power takes place between inductor and supply line
c. exchange of power takes place between capacitor and supply line
d. exchange of power does not take place between resistance and the supply line
e. all above are correct
Answer  Explanation 

ANSWER: all above are correct

Explanation:
No explanation is available for this question!


17)   If resistance is 20 Q. and inductance is 27 in a R-L series circuit, then time constant of this circuit will be________?

a. 0.001 s
b. 0.1 s
c. 10 s
d. 100 s
Answer  Explanation 

ANSWER: 0.1 s

Explanation:
No explanation is available for this question!


18)   The safest value of current the human body can carry for more than 3 second is_________?

a. 4 mA
b. 9 mA
c. 15 mA
d. 25 mA
Answer  Explanation 

ANSWER: 9 mA

Explanation:
No explanation is available for this question!


19)   Time constant of a circuit is the time in seconds taken after the application of voltage to each___________?

a. 25% of maximum value
b. 50% of maximum value
c. 63% of maximum value
d. 90% of the maximum value
Answer  Explanation 

ANSWER: 63% of maximum value

Explanation:
No explanation is available for this question!


20)   Power factor of electric bulb is__________?

a. zero
b. lagging
c. leading
d. unity
Answer  Explanation 

ANSWER: unity

Explanation:
No explanation is available for this question!