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.
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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.
