BEE DC and AC Circuit Analysis 4 — Questions and Answers
Question 1: A Wheatstone bridge is balanced when which condition is satisfied?
- R1/R2 = R3/R4 (Correct answer)
- R1 + R2 = R3 + R4
- R1 × R2 = R3 × R4
- R1 - R2 = R3 - R4
Correct answer: R1/R2 = R3/R4
A Wheatstone bridge is balanced (galvanometer reads zero) when the ratio of resistances in each arm satisfies R1/R2 = R3/R4.
Question 2: What is the significance of the Q-factor (quality factor) in a resonant circuit?
- It measures the sharpness of resonance and energy storage efficiency (Correct answer)
- It measures total power dissipation
- It indicates the phase angle of the circuit
- It represents the ratio of resistance to reactance
Correct answer: It measures the sharpness of resonance and energy storage efficiency
Q = ω₀L/R (series) represents the ratio of energy stored to energy dissipated per cycle, indicating how sharp the resonance peak is.
Question 3: In a DC transient RL circuit, how many time constants does it take for the current to reach approximately 99.3% of its steady-state value?
- 5τ (Correct answer)
- 1τ
- 3τ
- 2τ
Correct answer: 5τ
After 5 time constants (5τ = 5L/R), the current reaches 1 - e⁻⁵ ≈ 99.3% of its final value, considered practically at steady state.
Question 4: For maximum power transfer from a source with Thevenin impedance Zth to a load ZL, what condition must hold in AC circuits?
- ZL = Zth* (complex conjugate) (Correct answer)
- ZL = Zth
- ZL = 0
- ZL = infinity
Correct answer: ZL = Zth* (complex conjugate)
Maximum power transfer in AC circuits requires ZL = Zth*, meaning the load impedance equals the complex conjugate of the source impedance.
Question 5: What is the apparent power in an AC circuit with Vrms = 120 V and Irms = 5 A?
- 600 VA (Correct answer)
- 600 W
- 480 VAR
- 720 VA
Correct answer: 600 VA
Apparent power S = Vrms × Irms = 120 × 5 = 600 VA, regardless of the power factor.
Question 6: Kirchhoff's Voltage Law (KVL) is based on which fundamental principle?
- Conservation of energy (Correct answer)
- Conservation of charge
- Faraday's law of induction
- Ohm's law
Correct answer: Conservation of energy
KVL states that the algebraic sum of all voltages around a closed loop equals zero, which reflects conservation of energy in the circuit.
Question 7: A sinusoidal voltage is expressed as v(t) = 170 sin(377t + 30°) V. What is its RMS value?
- 120.2 V (Correct answer)
- 170 V
- 85 V
- 240 V
Correct answer: 120.2 V
For a sinusoidal waveform, Vrms = Vpeak / √2 = 170 / 1.414 ≈ 120.2 V.
BEE DC and AC Circuit Analysis 4
A Wheatstone bridge is balanced when which condition is satisfied?