ISCET Electronic Components & Circuit Analysis 4 — Questions and Answers
Question 1: Two resistors of 6 kΩ and 3 kΩ are connected in parallel. What is the equivalent resistance?
- 9 kΩ
- 4.5 kΩ
- 2 kΩ (Correct answer)
- 1.5 kΩ
Correct answer: 2 kΩ
Parallel resistance: 1/Req = 1/6k + 1/3k = 1/6k + 2/6k = 3/6k, so Req = 2 kΩ.
Question 2: What is the impedance of a pure inductor at DC (0 Hz)?
- Infinite
- Equal to its inductance in ohms
- Zero (Correct answer)
- Equal to its DC resistance only
Correct answer: Zero
Inductive reactance XL = 2πfL equals zero at DC (f = 0 Hz), so a pure inductor is a short circuit at DC.
Question 3: In a BJT, the current gain β (beta) is defined as:
- IC / IB (Correct answer)
- IE / IB
- IC / IE
- IB / IC
Correct answer: IC / IB
Beta (β or hFE) is the ratio of collector current to base current, typically ranging from 20 to 500 for common transistors.
Question 4: An electrolytic capacitor is installed with reversed polarity in a DC circuit. What will most likely occur?
- It will work normally but with reduced capacitance
- It will act as a resistor
- It may overheat and fail catastrophically (Correct answer)
- It will simply block current flow
Correct answer: It may overheat and fail catastrophically
Electrolytic capacitors are polarized; reverse polarity breaks down the oxide dielectric layer, causing excessive leakage current, heat, and possible explosion.
Question 5: What is the resonant frequency of a circuit with L = 10 mH and C = 10 μF?
- 159 Hz
- 503 Hz (Correct answer)
- 1592 Hz
- 5033 Hz
Correct answer: 503 Hz
fr = 1 / (2π√LC) = 1 / (2π√(0.01 × 0.00001)) = 1 / (2π × 3.16×10⁻⁴) ≈ 503 Hz.
Question 6: Which diode characteristic curve region allows the diode to be used as a variable capacitor (varactor)?
- Forward bias region
- Reverse bias region below breakdown (Correct answer)
- Zener breakdown region
- Avalanche breakdown region
Correct answer: Reverse bias region below breakdown
In the reverse-bias region, the depletion layer width varies with voltage, creating a voltage-controlled junction capacitance used in varactor (varicap) diodes.
Question 7: Kirchhoff's Voltage Law (KVL) states that:
- The sum of currents entering a node equals the sum leaving
- The algebraic sum of voltages around any closed loop equals zero (Correct answer)
- Voltage across parallel branches is always equal
- Total resistance in a loop equals total voltage divided by current
Correct answer: The algebraic sum of voltages around any closed loop equals zero
KVL states that the sum of all EMFs and voltage drops around any closed loop in a circuit equals zero, based on conservation of energy.
ISCET Electronic Components & Circuit Analysis 4
Two resistors of 6 kΩ and 3 kΩ are connected in parallel.
What is the equivalent resistance?