CET CET Analog Electronics and Amplifiers 2 — Questions and Answers
Question 1: What is the cutoff frequency of a first-order RC low-pass filter with R = 10 kΩ and C = 0.01 µF?
- 1.59 kHz (Correct answer)
- 15.9 kHz
- 159 Hz
- 15.9 MHz
Correct answer: 1.59 kHz
f = 1/(2πRC) = 1/(2π × 10,000 × 0.00000001) ≈ 1,592 Hz ≈ 1.59 kHz.
Question 2: An inverting op-amp amplifier has a feedback resistor Rf = 10 kΩ and input resistor Rin = 2 kΩ. What is the closed-loop voltage gain?
- -5 (Correct answer)
- +5
- -2
- +0.2
Correct answer: -5
Inverting amplifier gain = -Rf/Rin = -10k/2k = -5.
Question 3: Which type of negative feedback increases input impedance and decreases output impedance in an amplifier?
- Voltage-series (series-shunt) feedback (Correct answer)
- Current-shunt feedback
- Voltage-shunt feedback
- Current-series feedback
Correct answer: Voltage-series (series-shunt) feedback
Voltage-series (series-shunt) feedback samples the output voltage and applies series feedback at the input, raising Zin and lowering Zout.
Question 4: What does the slew rate of an op-amp specify?
- The maximum rate of change of output voltage in V/µs (Correct answer)
- The maximum output current in mA
- The minimum supply voltage in volts
- The gain-bandwidth product in MHz
Correct answer: The maximum rate of change of output voltage in V/µs
Slew rate defines the fastest the output voltage can change, expressed in volts per microsecond.
Question 5: Which amplifier class has the highest theoretical DC-to-output efficiency, reaching up to 78.5% for a sinusoidal signal?
- Class B (Correct answer)
- Class A
- Class AB
- Class C
Correct answer: Class B
Class B push-pull amplifiers have a theoretical maximum efficiency of 78.5% because each transistor conducts only 180° of the cycle.
Question 6: What is the primary purpose of coupling capacitors between amplifier stages?
- Pass AC signals while blocking DC bias levels between stages (Correct answer)
- Increase voltage gain
- Stabilize the operating point
- Filter high-frequency noise
Correct answer: Pass AC signals while blocking DC bias levels between stages
Coupling capacitors block DC so each stage maintains its own independent bias, while passing the AC signal to the next stage.
CET CET Analog Electronics and Amplifiers 2
What is the cutoff frequency of a first-order RC low-pass filter with R = 10 kΩ and C = 0.01 µF?