The input impedance of an op-amp in an ideal configuration is assumed to be:
Answer: A
Ideal op-amp assumptions include infinite input impedance (no current drawn at inputs), zero output impedance, and infinite open-loop gain.
Q.22Easy
In a Common Emitter BJT amplifier, if the collector resistance is increased while keeping other parameters constant, how does the voltage gain change?
Answer: A
Voltage gain Av = -gm × Rc, where gm is transconductance and Rc is collector resistance. Increasing Rc directly increases voltage gain.
Q.23Easy
A non-inverting amplifier is constructed with an op-amp having open-loop gain A₀ = 100,000. If Rf = 90 kΩ and Rin = 10 kΩ, what is the closed-loop voltage gain?
What is the primary advantage of a Darlington pair configuration in BJT amplifiers?
Answer: A
Darlington pairs consist of two transistors in cascade, providing extremely high current gain (β² product) and very high input impedance due to the two base-emitter junctions.
Q.25Easy
A BJT is operated in the saturation region. Which of the following statements is true?
Answer: B
In saturation, both junctions are forward biased: base-emitter junction is forward biased for current conduction, and base-collector junction is also forward biased, allowing maximum collector current.
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Q.26Easy
In a two-stage cascaded amplifier, the first stage has gain A₁ = 50 and bandwidth BW₁ = 100 kHz, while the second stage has A₂ = 20 and BW₂ = 200 kHz. What is the overall voltage gain?
Answer: B
In cascaded amplifiers, overall voltage gain = A₁ × A₂ = 50 × 20 = 1000. The bandwidth is determined by the stage with lowest bandwidth (100 kHz).
Q.27Easy
A voltage-controlled voltage source (VCVS) has transconductance gm = 50 mS. If the input voltage is 10 mV, what is the output current?
Answer: A
Output current Id = gm × Vgs = 50 mS × 10 mV = 50 × 10⁻³ × 10 × 10⁻³ = 0.5 × 10⁻³ A = 0.5 mA
Q.28Easy
What is the typical input impedance of a voltage follower (unity gain buffer) using an ideal op-amp?
Answer: B
An ideal op-amp has infinite input impedance. The voltage follower configuration maintains this high input impedance at the non-inverting input.
Q.29Easy
For maximum power transfer from a source with internal resistance Rs to load RL, what should be the condition?
Answer: B
Maximum power transfer theorem states that maximum power is delivered when load impedance equals the complex conjugate of source impedance. For resistive cases, RL = Rs.
Q.30Easy
What is the input offset voltage of a typical precision op-amp (like OP07)?
Answer: C
Precision op-amps like OP07, OPA2134 are designed with input offset voltages < 1 mV. General purpose op-amps (e.g., 741) have offset voltages of 1-5 mV.
Q.31Easy
What is the slew rate of a standard 741 op-amp?
Answer: A
The 741 op-amp has a slew rate of approximately 0.5 V/μs. This limits the maximum output voltage change rate, causing distortion at high frequencies/amplitudes.
Q.32Easy
What is the gain-bandwidth product (GBW) of a typical 741 op-amp?
Answer: A
The 741 op-amp has a gain-bandwidth product of approximately 1 MHz. This means for a gain of 100 V/V, maximum usable bandwidth is ~10 kHz.
Q.33Easy
What is the bandwidth of a first-order low-pass filter with cutoff frequency fc = 1 kHz?
Answer: B
Bandwidth of a low-pass filter is defined by its cutoff frequency (-3dB point). At f = fc, magnitude drops to 0.707 of DC gain. Bandwidth = fc = 1 kHz.
