21. In an RLC series circuit with constant voltage source but of frequency varying from zero to infinity, the circuit is said to be in electrical resonance when

- magnitude of X
_{L}> X_{C}and Z ≠ R - magnitude of X
_{L}= X_{C}and Z ≠ R - magnitude of X
_{L}= X_{C}and Z = R - magnitude of X
_{L}< X_{C}and Z ≠ R

22. Q- meter is based on characteristics of

- Parallel resonant circuit
- Series parallel circuit
- Series parallel circuit
- Inductive reactance circuit

23. Q-factor is defined as the ratio of

- Resistance/inductance of reactive element
- Resistance/capacitance of reactive element
- Resistance to reactance of reactive element
- Resistance to susceptance of reactive element

24. A choke coil having resistance R ohm and of inductance henry is shunted by a capacitor of C farads. The dynamic impedance of the resonant circuit would be

- R/LC
- C/RL
- L/RC
- 1/RLC

25. Magnitude of current at resonance in R-L-C circuit

- Depends upon magnitude of R
- Depending upon magnitude of L
- Depends upon magnitude of C
- Depends upon magnitude of R, L and C

26. If a parallel resonant circuit is shunted by resistance, then

- The circuit impedance is increased
- Q of the circuit is increased
- The gain of the circuit is increased
- The circuit impedance is decreased

27. The Exponential damping coefficient alpha is given by

- 1/2 RC for a parallel RLC circuit
- 2RC for a series RLC circuit
- R/2L for a parallel RLC circuit
- 2L/R for a series RLC circuit

28. A series RLC circuit is in resonance at 100Hz. If capacitance is made four times, the resonant frequency will be

- 50 Hz
- 100 Hz
- 200 Hz
- 400 Hz

29. If Q of a coil is increased, its power factor will

- Decrease
- Increase
- Remains same
- None of these

30. A resonance curve for a series circuit is a plot of frequency versus

- current
- voltage
- impedance
- reactance