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.
Which parameter is most important for selecting a heat sink for a power transistor?
Answer: B
Thermal resistance θJA (junction to ambient) determines how effectively heat is dissipated. Lower θJA values indicate better heat dissipation capability, essential for power dissipation calculations: Tj = Ta + (P × θJA).
Q.2Medium
In a MOSFET, what does the threshold voltage (Vth) represent?
Answer: B
Threshold voltage (Vth) is the minimum gate-source voltage required to create an inversion layer and form a conducting channel between drain and source in a MOSFET.
Q.3Medium
A photodiode is primarily used for:
Answer: C
Photodiodes operate in reverse bias and generate photocurrent proportional to incident light intensity. They are used in optical communication systems, light sensors, and imaging applications.
Q.4Medium
In a JFET, the pinch-off voltage (Vp) is the gate-source voltage at which:
Answer: B
Pinch-off voltage (Vp) for a JFET is the reverse gate-source voltage magnitude at which the channel becomes completely depleted, causing drain current to drop to approximately zero.
Q.5Medium
What is the maximum collector-emitter voltage rating (Vceo) used for?
Answer: B
VCEO (max) is a critical parameter specifying the maximum collector-emitter voltage the transistor can withstand without avalanche breakdown. Exceeding this rating can permanently damage the device.
Q.6Medium
A varactor diode is used primarily for:
Answer: C
Varactor (variable capacitor) diodes are reverse-biased devices whose junction capacitance varies with applied voltage. They are used in voltage-controlled oscillators, frequency modulators, and tuning circuits.
Q.7Medium
In a triode vacuum tube, which electrode controls the flow of electrons?
Answer: C
In a triode, the grid (control electrode) placed between cathode and anode controls electron flow through electrostatic fields, enabling amplification of signals applied to the grid.
Q.8Medium
In a p-n junction diode, the depletion region width depends on which of the following factors?
Answer: A
Depletion width W = √(2εV/qNd·Na/(Nd+Na)), dependent on applied voltage and doping concentrations.
Q.9Medium
A PIN diode is primarily used in high-frequency applications because:
Answer: B
PIN diodes have wide intrinsic region that reduces capacitance while increasing carrier transit time, ideal for RF switching.
Q.10Medium
In a BJT operating in the active region, which relationship holds true?
Answer: B
Active region requires base-emitter junction forward biased (~0.7V) and collector-base reverse biased (VCE > saturation voltage).
Q.11Medium
In a CMOS inverter, the power dissipation is primarily due to:
Answer: C
CMOS dynamic power = CV²f dominates; ideal CMOS has zero static power as pull-up and pull-down never conduct simultaneously.
Q.12Medium
The gain-bandwidth product (GBP) of a BJT is approximately equal to:
Answer: C
GBW ≈ fT; BJT current gain drops with frequency as β·f ≈ constant, where fT is extrapolated cutoff frequency (~1GHz for silicon BJTs).
Q.13Medium
Channel length modulation in MOSFETs causes:
Answer: B
CLM: as VDS increases, pinch-off point moves toward source, reducing effective channel length; output resistance Rds = VA/ID = λ⁻¹.
Q.14Medium
In a photodiode, the photocurrent is proportional to:
Answer: B
Photodiode: Iph = η·q·Φ where η is quantum efficiency and Φ is incident photon flux; reverse bias increases depletion width for carrier collection.
Q.15Medium
In a thyristor (SCR), the holding current (IH) is important because:
Answer: B
Holding current IH: minimum anode current to sustain regenerative action (latching); if IA < IH, device reverts to blocking state.
Q.16Medium
A MOSFET operating in triode (linear) region exhibits:
Answer: B
In triode region, the condition VDS < VGS - VTh allows the channel to conduct with resistance proportional to VDS.
Q.17Medium
Which statement correctly describes the Early effect in BJTs?
Answer: B
Early voltage (VA) is a parameter that depends on the base width modulation effect with collector-base reverse bias voltage.
Q.18Medium
In a Zener diode regulation circuit, increasing load current causes:
Answer: B
As load current increases, less current flows through the Zener diode to maintain constant output voltage, so Zener current decreases.
Q.19Medium
A Schottky diode compared to a pn-junction diode has:
Answer: B
Schottky diodes have forward voltage ~0.3-0.4V (vs 0.7V for Si) and fast switching due to no stored charge in depletion region.
Q.20Medium
The breakdown mechanism in a Zener diode at low doping concentrations is primarily:
Answer: A
Low doping leads to wide depletion region favoring avalanche breakdown (impact ionization) rather than direct Zener tunneling.
