BEE Electric Circuits 4 — Questions and Answers
Question 1: A circuit has an impedance Z = 3 + j4 Ω. What is the magnitude of the impedance?
- 5 Ω (Correct answer)
- 7 Ω
- 4 Ω
- 3.5 Ω
Correct answer: 5 Ω
|Z| = √(3² + 4²) = √(9 + 16) = √25 = 5 Ω.
Question 2: In mesh analysis, a mesh current is defined as a current flowing:
- Around a single closed loop (mesh) of the circuit (Correct answer)
- Through a single resistor
- Into a node
- Through the external source
Correct answer: Around a single closed loop (mesh) of the circuit
Mesh analysis assigns a circulating current variable to each independent mesh (window pane) in the circuit.
Question 3: What happens to the capacitive reactance XC as frequency increases?
- XC decreases (Correct answer)
- XC increases
- XC remains constant
- XC becomes purely resistive
Correct answer: XC decreases
Capacitive reactance XC = 1/(2πfC), so as frequency increases, XC decreases.
Question 4: Which theorem states that maximum power is transferred to a load when the load resistance equals the source's Thevenin resistance?
- Maximum Power Transfer Theorem (Correct answer)
- Norton's Theorem
- Superposition Theorem
- Millman's Theorem
Correct answer: Maximum Power Transfer Theorem
The Maximum Power Transfer Theorem states that PL is maximum when RL = Rth.
Question 5: The quality factor Q of a series RLC circuit is defined as:
- ω₀L / R (Correct answer)
- R / ω₀L
- ω₀C / R
- R × ω₀L
Correct answer: ω₀L / R
For a series RLC circuit, Q = ω₀L/R = 1/(ω₀CR), representing the ratio of stored to dissipated energy.
Question 6: A voltage divider has R1 = 4 kΩ and R2 = 1 kΩ connected to a 10 V source. What is the voltage across R2?
- 2 V (Correct answer)
- 8 V
- 5 V
- 4 V
Correct answer: 2 V
Voltage divider: V2 = 10 × R2/(R1+R2) = 10 × 1/(4+1) = 2 V.
Question 7: In an AC circuit, reactive power Q is measured in:
- Volt-Ampere Reactive (VAR) (Correct answer)
- Watts (W)
- Volt-Ampere (VA)
- Joules (J)
Correct answer: Volt-Ampere Reactive (VAR)
Reactive power, which represents energy oscillating between source and reactive elements, is measured in VAR.
BEE Electric Circuits 4
A circuit has an impedance Z = 3 + j4 Ω.
What is the magnitude of the impedance?