Electronics and Communication questions reward anyone who is comfortable moving between the time domain and the frequency domain. This set covers network theory, analog and digital circuits, signals and systems, control systems, communication systems, and electromagnetics. Numerical solutions keep the units visible at every step, since a dropped factor is the most common reason a correct method still produces a wrong option.
In a Common Source FET amplifier, the gain is primarily dependent on which parameter?
Answer: A
The voltage gain of a CS amplifier is Av = -gm × RD, where gm is transconductance and RD is the drain resistance. This is the fundamental relationship.
Q.242Easy
A BJT amplifier operates in the saturation region. What is the approximate output impedance?
Answer: B
In saturation, the transistor acts almost like a closed switch with minimal voltage drop across it, resulting in very low output impedance.
Q.243Easy
The input impedance of a Common Emitter amplifier is approximately equal to:
Answer: A
The input impedance of a CE amplifier is Zin ≈ β × re, where β is current gain and re is emitter resistance (≈ VT/IE).
Q.244Easy
In a differential amplifier, the Common Mode Rejection Ratio (CMRR) is 80 dB. What is the CMRR in linear form?
A voltage follower (Common Collector) amplifier has a voltage gain of:
Answer: A
The voltage gain of a voltage follower is Av ≈ 1 (or slightly less due to emitter resistance effects). It is used for impedance matching.
Q.246Medium
An op-amp has an open-loop gain of 100,000 and a feedback resistor ratio of Rf/Rin = 10. What is the closed-loop gain?
Answer: A
For a non-inverting amplifier, Acl ≈ 1 + (Rf/Rin) = 1 + 10 = 11. The feedback dominates over the open-loop gain.
Q.247Medium
In a Colpitts oscillator, the feedback network consists of:
Answer: A
Colpitts oscillator uses capacitive voltage divider with two capacitors in series across an inductor for frequency-determining feedback.
Q.248Medium
A Class B power amplifier has two transistors. What is the primary advantage over Class A?
Answer: A
Class B achieves ~78.5% efficiency by conducting only 180° of the cycle compared to Class A's ~25% efficiency, though it introduces crossover distortion.
Q.249Medium
In a push-pull amplifier configuration, what is the phase relationship between the two transistor inputs?
Answer: A
Push-pull amplifiers use complementary transistors driven 180° out of phase to handle positive and negative half-cycles separately.
Q.250Medium
An inverting amplifier has Rin = 10 kΩ and Rf = 100 kΩ. If the input signal is 100 mV, what is the output voltage?
Answer: A
For inverting amplifier, Vo = -(Rf/Rin) × Vin = -(100k/10k) × 0.1 = -10 × 0.1 = -1 V.
Q.251Easy
In a BJT amplifier biased in the active region, what is the relationship between collector current and base current?
Answer: A
In the active region, IC = β × IB where β is the DC current gain (typically 50-300 for silicon BJTs).
Q.252Medium
Which parameter primarily determines the frequency stability of an RC oscillator?
Answer: A
RC oscillators derive their frequency from RC time constants. The frequency f = 1/(2πRC) approximately, making RC the dominant parameter.
Q.253Easy
An op-amp integrator circuit has R = 10 kΩ and C = 100 nF. What is the time constant?
Answer: A
Time constant τ = RC = 10×10³ × 100×10⁻⁹ = 10×10⁻⁴ = 1×10⁻³ s = 1 ms.
Q.254Hard
In a Common Gate FET amplifier, how does the input impedance compare to Common Source?
Answer: A
CG configuration has low input impedance ≈ 1/gm because the input is presented at the source terminal, acting as a transimpedance amplifier.
Q.255Easy
The gain-bandwidth product (GBW) of a typical general-purpose op-amp (like LM741) is approximately:
Answer: A
LM741 has a GBW product of approximately 1 MHz, which is why it's limited to low-frequency applications. Modern op-amps have higher GBW.
Q.256Hard
In a feedback amplifier with loop gain L = Aβ, the closed-loop gain is approximately:
Answer: A
For negative feedback, Acl = A/(1+L) where L = Aβ is the loop gain. This formula shows how feedback reduces gain but improves stability.
Q.257Medium
A Class AB amplifier operates with a quiescent current (ICQ) that is:
Answer: A
Class AB uses a small quiescent current to bias transistors slightly into conduction, eliminating crossover distortion while maintaining better efficiency than Class A.
Q.258Easy
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.259Easy
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.260Easy
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?
