This set of Basic Electrical Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Alternating Current in an RLC Circuit”.

1. Find the total voltage applied in a series RLC circuit when i=3mA, VL=30V, VC=18V and R=1000 ohms.

a) 3.95V

b) 51V

c) 32.67V

d) 6.67V

View Answer

Explanation: Total voltage= VR+VL+VC.

VR=1000*3*10

^{-3}=3V. Therefore, total voltage= 30+18+3=51V.

2. In an RLC circuit, which of the following is always used as a vector reference?

a) Voltage

b) Resistance

c) Impedance

d) Current

View Answer

Explanation: In an RLC circuit, the voltage is always used as a reference and according to the phase of the voltage, the phase of the other parameters is decided.

3. In an RLC circuit, the power factor is always ____________

a) Positive

b) Negative

c) Depends on the circuit

d) Zero

View Answer

Explanation: In an RLC series circuit, the power factor depends on the number of resistors and inductors in the circuit, hence it depends on the circuit.

4. In an RLC series phasor, we start drawing the phasor from which quantity?

a) Voltage

b) Resistance

c) Impedance

d) Current

View Answer

Explanation: In an RLC series phasor diagram, we start drawing the phasor from the quantity which is common to all three components, that is the current.

5. What is the correct expression for the phase angle in an RLC series circuit?

a) φ=tan^{-1}(XL-XC)/R

b) φ=tan^{-1} (XL+XC)/R

c) φ=tan(XL-XC)/R

d) φ=tan^{-1} (XL-XC)

View Answer

Explanation: from the impedance triangle we get tanφ=(XL-XC)/R.

Hence φ=tan

^{-1}(XL-XC)/R.

6. When is tanφ positive?

a) When inductive reactance is less than capacitive reactance

b) When inductive reactance is greater than capacitive reactance

c) When inductive reactance is equal to capacitive reactance

d) When inductive reactance is zero

View Answer

Explanation: tanφ is positive when inductive reactance is greater than capacitive reactance because current will lag the voltage.

7. When is tanφ negative?

a) When inductive reactance is less than capacitive reactance

b) When inductive reactance is greater than capacitive reactance

c) When inductive reactance is equal to capacitive reactance

d) When inductive reactance is zero

View Answer

Explanation: tanφ is positive when inductive reactance is less than capacitive reactance because current will lead the voltage.

8. When is current in phase with the voltage?

a) When XL>XC

b) When XL<XC

c) When XL=XC

d) When XC=infinity

View Answer

Explanation: The current is in phase with the voltage when the capacitive reactance is in phase with the inductive reactance.

9. What is resonance condition?

a) When XL>XC

b) When XL<XC

c) When XL=XC

d) When XC=infinity

View Answer

Explanation: The current is in phase with the voltage when the capacitive reactance is in phase with the inductive reactance. This is known as resonance condition.

10. What is the frequency in resonance condition?

a) Minimum

b) Maximum

c) Cannot be determined

d) Zero

View Answer

Explanation: At resonance condition, the frequency is maximum since the inductive reactance is equal to the capacitive reactance and the voltage and current are in phase.

**Sanfoundry Global Education & Learning Series – Basic Electrical Engineering.**

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