21. A resistance of 7 ohms is connected in series with an inductance of 31.8mH. The circuit is connected to an x V 50Hz sinusoidal supply. The current in the circuit is 8.2A. Calculate the value of x.

A. 10 V

B. 50 V

C. 100 V

D. 120 V

22. Which among the following is the correct expression for φ?

A. φ = tan^{-1} (XL/R)

B. φ = tan^{-1} (R/XL)

C. φ = tan^{-1} (XL × R)

D. φ = cos^{-1} (XL/R)

23. For an RL circuit, the phase angle is always ________

A. Positive

B. Negative

C. 0

D. 90

24. What is φ in terms of voltage?

A. φ = cos^{-1}V/VR

B. φ = cos^{-1}V × VR

C. φ = cos^{-1}VR/V

D. φ = tan^{-1}V/VR

25. What is sinϕ from the impedance triangle?

A. X_{L}/R

B. X_{L}/Z

C. R/Z

D. Z/R

26. What is the resonance frequency of ac circuit?

A. 1/√LC

B. √(L/C.

C. √LC

D. LC

27. What is impedance at resonance?

A. maximum

B. minimum

C. zero

D. cannot be determined

28. What is the value of impedance at resonance?

A. X_{L}

B. X_{C}

C. R

D. 0

29. What is φ in terms of voltage?

A. φ = cos^{-1}V/V_{R}

B. φ = cos^{-1}V × V_{R}

C. φ = cos^{-1}V_{R}/V

D. φ = tan^{-1}V/V_{R}

30. What is tanϕ for the RC circuit?

A. X_{C}/R

B. X_{L}/R

C. R/Z

D. Z/R