Friday, September 4, 2020

Chapter 4: Complex AC Circuits- Page 2

Chapter 4: Complex AC Circuits

11. The purpose of choke in a flourescent tube is
A. to decrease the voltage momentarily
B. to increase the voltage momentarily
C. to decrease the current
D. to increase the current

... Answer is (B)



12. The power factor of an a.c. circuit is given by

B. Z/R
D. R/Z

... Answer is (D)


13. The active and reactive components of line current of an inductive circuit are equal. The power factor of the circuit is

A. 0.5 lagging
B. 0.866 lagging

D. 0.707 lagging

... Answer is (D)



14. In an R-L series circuit, the two sides of the impedance triangle that form the phase angle are

A. Z and XL
B. R and XL
C. R and Z
D. none of the above

  ... Answer is (C)


15. If in an R-L-C series circuit, the frequency is below the resonant frequency, then
Answer is (C)


16. At series resonance,
voltage across L or C is zero
B. circuit power factor is unity

circuit impedance is very large
D. circuit power factor is minimum

  ... Answer is (B)



17. At series resonance, the voltage across L or C is

A. much more than applied voltage
B. equal to voltage across R

equal to applied voltage
D. less than applied voltage

... Answer is (A)


18. The Q factor of a coil is resistance of coil.  

A. Independent of
inversely proportional to
C. directly proportional to

D. None of the above

... Answer is (B)


19. An R-L-C series circuit is connected to a 200 V a.c. source. If Q factor of the coil is 10, then voltage across C at resonance is

A. 20 V
B. 210 V
C. 200 V
D. 2000 V
  ... Answer is (D)


20.  A coil is supplied with 200 V and takes a current of 2A at 45° lagging. The Q of the coil is

B. 10

D. 100

  ... Answer is (A)



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