The most important and relevant **AC fundamentals MCQs** in Electrical Engineering.

**AC fundamentals MCQs**

**The form factor is the ratio of ?**

A. peak value to r.m.s. value

B. r.m.s. value to average value

C. average value to r.m.s. value

D. none of the above

**B. r.m.s. value to average value**

**The period of a wave is ?**

A. the same as frequency

B. time required to complete one cycle

C. expressed in amperes

D. none of the above

**B. time required to complete one cycle**

**In a series resonant circuit the impedance of the circuit is ?**

A. minimum

B. maximum

C. zero

D. none of the above

**A. minimum**

**Pure inductive circuit ?**

A. consumes some power on average

B. does not take power at all from a line

C. takes power from the line during some part of the cycle and then returns back to it during other part of the cycle

D. none of the above

**C. takes power from the line during some part of the cycle and then returns back to it during other part of the cycle**

**In a pure inductive circuit ?**

A. the current is in phase with the voltage

B. the current lags behind the voltage by 90°

C. the current leads the voltage by 90°

D. the current can lead or lag by 90°

**B. the current lags behind the voltage by 90°**

**The frequency of an alternating current is ?**

A. the speed with which the alternator runs

B. the number of cycles generated in one minute

C. the number of waves passing through a point in one second

D. the number of electrons passing through a point in one second

**C. the number of waves passing through a point in one second**

**AC fundamentals MCQs**

**In a pure inductive circuit the power is ?**

A. actual power is zero

B. reactive power is zero

C. apparent power is zero

D. none of above is zero

**A. actual power is zero**

**Inductance of coil ?**

A. is unaffected by the supply frequency

B. decreases with the increase in supply frequency

C. increases with the increase in supply frequency

D. becomes zero with the increase in supply frequency

**C. increases with the increase in supply frequency**

**Power factor of the following circuit will be unity ?**

A. inductance

B. capacitance

C. resistance

D. both A and B

**C. resistance**

**The peak value of a sine wave is 200 V. Its average value is ?**

A. 127.4 V

B. 141.4 V

C. 282.8 V

D. 200 V

**B. 141.4 V**

**A sine wave has a frequency of 50 Hz. Its angular frequency is ________ radian/second ?**

A. 100 n

B. 50 JT

C. 25 JT

D. 5 n

**A. 100 n**

**Power factor of an electrical circuit is equal to ?**

A. R/Z

B. cosine of phase angle difference be-tween current and voltage

C. kW/kVA

D. ratio of useful current to total current Iw/I

E. all of these

**E. all of these**

**AC fundamentals MCQs**

**The voltage of domestic supply is 220V. This figure represents ?**

A. mean value

B. r.m.s. value

C. peak value

D. average value

**A. mean value**

**The best place to install a capacitor is ?**

A. very near to inductive load

B. across the terminals of the inductive load

C. far away from the inductive load

D. any where

**B. across the terminals of the inductive load**

**All the rules and laws of D.C. circuit also apply to A.C. circuit containing ?**

A. capacitance only

B. inductance only

C. resistance only

D. all above

**C. resistance only**

**For a frequency of 200 Hz the time period will be ?**

A. 0.05 s

B. 0.005 s

C. 0.0005 s

D. 0.5 s

**B. 0.005 s**

**Capacitive reactance is more when ?**

A. capacitance is less and frequency of supply is less

B. capacitance is less and frequency of supply is more

C. capacitance is more and frequency of supply is less

D. capacitance is more and frequency of supply is more

**A. capacitance is less and frequency of supply is less**

**Poor power factor ?**

A. reduces load handling capability of electrical system

B. results in more power losses in the electrical system

C. overloads alternators, transformers and distribution lines

D. results in more voltage drop in the line

E. results in all above

**E. results in all above**

**AC fundamentals MCQs**

**Form factor for a sine wave is ?**

A. 1.414

B. 0.707

C. 1.11

D. 0.637

**C. 1.11**

**For a sine wave with peak value Imax the r.m.s. value is ?**

A. 0.5 Imax

B. 0.707

C. 0.9

D. 1.414 Lmax

**B. 0.707**

**In a highly capacitive circuit the ?**

A. apparent power is equal to the actual power

B. reactive power is more than the apparent power

C. reactive power is more than the actual power

D. actual power is more than its reactive power

**C. reactive power is more than the actual power**

**Power factor of the following circuit will be zero ?**

A. resistance

B. inductance

C. capacitance

D. both B and C

**D. both B and C**

**Capacitors for power factor correction are rated in ?**

A. kW

B. kVA

C. kV

D. kVAR

**D. kVAR**

**Power factor of the system is kept high ?**

A. to reduce line losses

B. to maximise the utilization of the capacities of generators, lines and transformers

C. to reduce voltage regulation of the line

D. due to all above reasons

**D. due to all above reasons**

**AC fundamentals MCQs**

**In a pure resistive circuit ?**

A. current lags behind the voltage by 90°

B. current leads the voltage by 90°

C. current can lead or lag the voltage by 90°

D. current is in phase with the voltage

**D. current is in phase with the voltage**

**The power factor of a D.C. circuit is always ?**

A. less than unity

B. unity

C. greater than unity

D. zero

**B. unity**

**The r.m.s. value of pure cosine function is ?**

A. 0.5 of peak value

B. 0.707 of peak value

C. same as peak value

D. zero

**B. 0.707 of peak value**

**In an A.C. circuit power is dissipated in ?**

A. resistance only

B. inductance only

C. capacitance only

D. none of the above

**A. resistance only**

**The inductance of a coil can be increased by ?**

A. increasing core length

B. decreasing the number of turns

C. decreasing the diameter of the former

D. choosing core material having high relative permeability

**D. choosing core material having high relative permeability**

**Which of the following refers to a parallel circuit ?**

A. The current through each element is same

B. The voltage across element is in proportion to it’s resistance value

C. The equivalent resistance is greater than any one of the resistors

D. The current through any one element is less than the source current

**D. The current through any one element is less than the source current**

**AC fundamentals MCQs**

**Capacitive susceptance is a measure of ?**

A. reactive power in a circuit

B. the extent of neutralisation of reactive power in a circuit

C. a purely capacitive circuit’s ability to pass current

D. a purely capacitive circuit’s ability to resist the flow of current

**C. a purely capacitive circuit’s ability to pass current**

**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

**A. can dissipate considerable amount of power**

**The purpose of a parallel circuit resonance is to magnify ?**

A. current

B. voltage

C. power

D. frequency

**B. voltage**

**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

**E. all above are correct**

**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

**B. have a high impedance**

**The ratio of active power to apparent power is known as factor ?**

A. demand

B. load

C. power

D. form

**C. power**

**AC fundamentals MCQs**

**Power factor of electric bulb is ?**

A. zero

B. lagging

C. leading

D. unity

**D. unity**

**Pure inductive circuit takes power from the A.C. line when ?**

A. applied voltage decreases but current increases

B. applied voltage increases but current decreases

C. both applied voltage and current increase

D. both applied voltage and current decrease

**A. applied voltage decreases but current increases**

**In any A.C. circuit always ?**

A. apparent power is more than actual power

B. reactive power is more than apparent power

C. actual power is more than reactive power

D. reactive power is more than actual power

**A. apparent power is more than actual power**

**Time constant of an inductive circuit ?**

A. increases with increase of inductance and decrease of resistance

B. increases with the increase of inductance and the increase of resistance

C. increases with decrease of inductance and decrease of resistance

D. increases with decrease of inductance and increase of resistance

**A. increases with increase of inductance and decrease of resistance**

**The r.m.s. value and mean value is the same in the case of ?**

A. triangular wave

B. sine wave

C. square wave

D. half wave rectified sine wave

**C. square wave**

**Inductance affects the direct current flow ?**

A. Only at the time of turning off

B. Only at the time of turning on

C. At the time of turning on and off

D. At all the time of operation

**C. At the time of turning on and off**

**AC fundamentals MCQs**

**In a loss-free R-L-C circuit the transient current is ?**

A. oscillating

B. square wave

C. sinusoidal

D. non-oscillating

**C. sinusoidal**

**At very low frequencies a series R-C circuit behaves as almost purely ?**

A. resistive

B. inductive

C. capacitive

D. none of the above

**C. capacitive**

**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

**D. exhibit unwanted inductive and capacitive effects**

**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

**C. A coil with large distributed capacitance**

**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

**B. 9 mA**

**The time constant of a series R-C circuit is given by ?**

A. R/C

B. RC2

C. RC

D. R2C

**C. RC**

**AC fundamentals MCQs**

**The time constant of a series R-C circuit is given by ?**

A. R/C

B. RC2

C. RC

D. R2C

**C. RC**

**Magnitude of current at resonance in R-L-C circuit ?**

A. depends upon the magnitude of R

B. depends upon the magnitude of L

C. depends upon the magnitude of C

D. depends upon the magnitude of R, Land C

**A. depends upon the magnitude of R**

**Time constant of an inductive circuit ?**

A. increases with increase of inductance and decrease of resistance

B. increases with the increase of inductance and the increase of resistance

C. increases with the decrease of inductance and decrease of resistance

D. increases with decrease of inductance and increase of resistance

**A. increases with increase of inductance and decrease of resistance**

**Time constant of a capacitive circuit ?**

A. increases with the decrease of capacitance and decrease of resistance

B. increases with the decrease of capacitance and increase of resistance

C. increases with the increase of capacitance and decrease of resistance

D. increase with increase of capacitance and increase of resistance

**D. increase with increase of capacitance and increase of resistance**

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