What is the primary function of a PN junction diode?
Answer: B
A PN junction diode exhibits rectification property, allowing current to flow easily in the forward direction (low resistance) and blocking it in the reverse direction (high resistance).
Q.2Easy
The barrier potential of a silicon PN junction at room temperature is approximately:
Answer: B
Silicon PN junctions have a built-in barrier potential of approximately 0.7 V at room temperature (25°C), while germanium junctions are around 0.3 V.
Q.3Easy
Which of the following is NOT a characteristic of a Zener diode?
Answer: C
Zener diodes have low forward resistance (like normal diodes in forward bias) but the unique property is controlled reverse breakdown at a specific voltage for regulation purposes.
Q.4Easy
In a BJT (Bipolar Junction Transistor), what are the three regions of operation?
Answer: B
BJT operates in three distinct regions: Active region (linear amplification with both junctions forward biased), Saturation (both junctions forward biased, acts as switch ON), and Cutoff (both junctions reverse biased, acts as switch OFF).
Q.5Easy
What is the relationship between collector current (Ic) and base current (Ib) in a BJT?
Answer: A
In BJT, the current gain (beta or hFE) is defined as the ratio of collector current to base current: β = Ic/Ib, so Ic = Ib × β. Beta typically ranges from 50 to 500 for most transistors.
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Q.6Easy
An LED (Light Emitting Diode) emits light when:
Answer: B
LEDs emit light through electroluminescence when forward biased with sufficient current. The energy of emitted photons equals the bandgap energy of the semiconductor material.
Q.7Medium
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.8Medium
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.9Medium
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.10Medium
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.11Medium
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.12Medium
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.13Medium
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.14Hard
A tunnel diode exhibits negative resistance in a specific voltage range due to:
Answer: D
Tunnel diodes show negative differential resistance due to quantum tunneling through the narrow depletion region created by heavy doping. This occurs in forward bias and enables their use as oscillators and amplifiers.
Q.15Hard
For a BJT in saturation, the relationship between base current and collector current is:
Answer: B
In saturation, both junctions are forward biased. The collector current becomes less than β × Ib because the transistor is no longer in linear region. Excess base current doesn't proportionally increase collector current.
Q.16Hard
Which of the following statements about CMOS logic is correct?
Answer: B
CMOS (Complementary MOS) has very low static power dissipation because complementary P and N transistors prevent steady-state current paths. However, dynamic power dissipation increases with switching frequency due to capacitive charging/discharging.
Q.17Hard
In a power MOSFET, the on-resistance (RDS_on) is primarily determined by:
Answer: C
RDS_on consists of channel resistance and drift region resistance. For power MOSFETs, drift region (epitaxial layer) dominates. Minimizing drift region thickness reduces RDS_on but decreases breakdown voltage, creating a design trade-off.
Q.18Hard
A Schottky diode offers advantages over PN junction diodes primarily because of:
Answer: C
Schottky diodes have metal-semiconductor junctions with lower forward voltage (0.3-0.5V vs 0.7V for silicon) and faster switching due to absence of minority carrier storage. This makes them ideal for high-frequency and high-speed switching applications.
Q.19Hard
What is the significance of Early voltage (VA) in a BJT?
Answer: C
Early voltage (VA) represents the output resistance (ro = VA/Ic) of a BJT. Larger VA indicates steeper output characteristics, meaning collector current is more independent of collector-emitter voltage, indicating better current source behavior.
Q.20Hard
In integrated circuit design, what does the term 'aspect ratio' refer to in MOSFETs?
Answer: B
Aspect ratio (W/L) is a fundamental design parameter in MOSFETs affecting current capability and switching speed. Higher W/L provides larger current capacity and faster transitions, crucial for circuit optimization and performance tuning.
