# Single Phase Series Circuit MCQ [Free PDF] – Objective Question Answer for Single Phase Series Circuit Quiz

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

XL = 2 × π × f × L = 10 ohm.

Z2 = (R2+XL2)

Therefore, the total impedance Z = 12.2ohm.

V = IZ

∴ V = 12.2 × 8.2 = 100V.

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)

From the impedance triangle, we get

tanφ = XL/R.

Hence φ = tan-1 (XL/R).

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

A. Positive
B. Negative
C. 0
D. 90

For a series resistance and inductance circuit, the phase angle is always a negative value because the current will always lag the voltage.

24. What is φ in terms of voltage?

A. φ = cos-1V/VR
B. φ = cos-1V × VR
C. φ = cos-1VR/V
D. φ = tan-1V/VR

From the voltage triangle, we get

cosφ = VR/V.

Hence φ = cos-1VR/V.

25. What is sinϕ from the impedance triangle?

A. XL/R
B. XL/Z
C. R/Z
D. Z/R

In the Impedance triangle, the Base is R, Hypotenuse is Z, and Height is XL.

So, sinϕ = XL/Z.

26. What is the resonance frequency of ac circuit?

A. 1/√LC
B. √(L/C.
C. √LC
D. LC

At resonance, XL = XC

ωL = 1/ωC

ω = 1/√LC

27. What is impedance at resonance?

A. maximum
B. minimum
C. zero
D. cannot be determined

At resonance, XL = XC

Z2 = R2+(XL-XC)2

Z = R So Z is minimum at resonance.

28. What is the value of impedance at resonance?

A. XL
B. XC
C. R
D. 0

At resonance, XL = XC

Z2 = R2+(XL-XC)2

Z = R So Z is minimum at resonance.

29. What is φ in terms of voltage?

A. φ = cos-1V/VR
B. φ = cos-1V × VR
C. φ = cos-1VR/V
D. φ = tan-1V/VR

From the voltage triangle, we get

cosφ = VR/V.

Hence φ = cos-1VR/V.

30. What is tanϕ for the RC circuit?

A. XC/R
B. XL/R
C. R/Z
D. Z/R