AC BASICS AND NETWORKS 1

AC BASICS AND NETWORKS

11. Unit of reactive power is
a) VA
b) watt
c) VAR
d) ohm
ans: c

12. An ac source of 200V RMS supplies active power of 600 W and reactive power of 800 VAR. The RMS current drawn from the source is
a) 10 A
b) 5 A
c) 3.75 A
d) 2.5 A
ans: b

13. With the increase in applied frequency, the dielectric loss in the material will
a) increase
b) decrease
c) remains constant
d) becomes zero
ans: a

14. In an ac series RLC circuit, the voltage across R and L is 20 V, the voltage across L and C is 9 V and voltage and voltage across RLC is 15 V, What is the voltage across C?
a) 7V
b) 12 V
c) 16 V
d) 21 V
ans: a

15. The quantity (2 + j9) represents the resistive and reactive components of current drawn by an ac circuit. The phase angle between the applied voltage and current is
a) 41.4'
b) 53.13'
c) 36.87'
d) 46.86'
ans: c

16. Under the condition resonance in the R-L-C series circuit, the pf of the circuit is
a) 0.5 lagging
b) 0.5 leading
c) unity
d) zero
ans: c

17. In a series RLC circuit at resonance, the magnitude of voltage developed across the capacitor
a) is always zero
b) can never be greater than the input voltage
c) can be greater than the input voltage however,  it is 90 degrees out of phase with the input voltage
d) can be greater than the input voltage and is in phase with the input voltage.
ans: c

18. In A series R-L-C circuit, the maximum voltage across the capacitor occurs at a frequency
a) double the resonant frequency
b) equal to the resonant frequency
c) below the resonant frequency
d) none of the above
ans: c

19. In a series R-L-C circuit, the voltage across inductance will be maximum
a) at the resonant frequency
b) just after resonant frequency
c) just before resonant frequency
d) just before and after resonant frequency
ans: b

20. For a series R-L-C circuit, the power factor at the lower power frequency is
a) 0.5 lagging
b) 0.5 leading
c) unity
d) 0.707 leading
ans: d