Section 1 - Electronic Devices and Circuits

Question 1

In a p-n junction diode under forward bias, the barrier potential:

A. Increases

B. Decreases

C. Remains constant

D. Becomes zero instantaneously

Question 2

The reverse saturation current in a p-n junction diode is mainly due to:

A. Majority carriers

B. Minority carriers

C. Both equally

D. Applied voltage magnitude

Question 3

In a Zener diode, the sharp increase in reverse current at breakdown is primarily due to:

A. Avalanche breakdown only

B. Zener breakdown only

C. Zener and/or avalanche mechanisms depending on doping

D. Thermal runaway

Question 4

The cut-in voltage for a silicon diode at room temperature is approximately:

A. 0.2 V

B. 0.3 V

C. 0.7 V

D. 1.1 V

Question 5

For a full-wave bridge rectifier with sinusoidal input, the ripple factor (without filter) is approximately:

A. 0.48

B. 0.81

C. 1.21

D. 1.57

Question 6

The peak inverse voltage (PIV) for a diode in a full-wave centre-tapped rectifier (each diode) is:

A. Vm

B. 2 Vm

C. Vm / 2

D. Vm / sqrt(2)

Question 7

In a common-emitter BJT amplifier, the phase shift between input and output signals is:

A. 0 degrees

B. 90 degrees

C. 180 degrees

D. 270 degrees

Question 8

The relationship between alpha and beta of a BJT is given by:

A. beta = alpha / (1 - alpha)

B. beta = alpha / (1 + alpha)

C. beta = 1 / alpha

D. beta = 1 - alpha

Question 9

For a BJT operating in the active region:

A. Both junctions are forward biased

B. Both junctions are reverse biased

C. Emitter-base junction is forward biased and collector-base junction is reverse biased

D. Emitter-base junction is reverse biased and collector-base junction is forward biased

Question 10

Which BJT biasing arrangement provides the best stability against changes in beta and temperature?

A. Fixed bias

B. Collector-to-base bias

C. Voltage-divider (self) bias

D. Emitter bias with a single supply

Question 11

The h-parameter h_fe of a BJT in common-emitter configuration represents:

A. Input impedance with output short-circuited

B. Reverse voltage ratio with input open-circuited

C. Forward current gain with output short-circuited

D. Output admittance with input open-circuited

Question 12

In a JFET, the pinch-off voltage is:

A. The gate-source voltage at which drain current becomes zero

B. The drain-source voltage at which the channel is fully constricted at the drain end

C. The maximum drain voltage before breakdown

D. The gate voltage at which the device is destroyed

Question 13

An enhancement-type n-channel MOSFET conducts when:

A. V_GS is negative and less than threshold

B. V_GS is zero

C. V_GS is positive and greater than the threshold voltage

D. V_DS is zero

Question 14

The transconductance g_m of a FET is defined as:

A. Change in drain current per unit change in gate-source voltage at constant V_DS

B. Change in gate voltage per unit change in drain current

C. Drain current divided by gate voltage

D. Change in drain-source voltage per unit change in drain current

Question 15

Which of the following statements about MOSFETs is correct?

A. MOSFETs have lower input impedance than BJTs

B. MOSFETs have very high input impedance due to the insulated gate

C. MOSFETs cannot be used as switches

D. MOSFETs conduct in only one polarity of V_DS

Question 16

A class A amplifier has a maximum theoretical efficiency of:

A. 25 percent (RC load)

B. 50 percent (transformer-coupled)

C. 78.5 percent

D. 100 percent

Question 17

A class B push-pull amplifier has a maximum theoretical efficiency of approximately:

A. 25 percent

B. 50 percent

C. 78.5 percent

D. 100 percent

Question 18

Crossover distortion is a problem associated with:

A. Class A amplifiers

B. Class B amplifiers

C. Class AB amplifiers only if biased incorrectly, but is inherent to class B

D. Class C amplifiers only

Question 19

Negative feedback in an amplifier:

A. Increases distortion and reduces bandwidth

B. Increases gain and increases noise

C. Reduces gain but improves bandwidth, stability, and distortion

D. Has no effect on bandwidth

Question 20

For sustained oscillations in a feedback oscillator, the Barkhausen criterion requires the loop gain magnitude to be:

A. Less than 1 with any phase shift

B. Exactly 1 with a total loop phase shift of 0 or 360 degrees

C. Greater than 1 with a phase shift of 180 degrees

D. Zero with any phase shift

Question 21

A Wien bridge oscillator is commonly used to generate:

A. Square waves at radio frequencies

B. Sinusoidal audio-frequency signals

C. Microwave oscillations

D. DC voltages

Question 22

A Colpitts oscillator uses feedback obtained from:

A. A tapped inductor

B. A capacitive voltage divider in the tank circuit

C. A resistive voltage divider

D. A crystal only

Question 23

A crystal oscillator is preferred over an LC oscillator when the primary requirement is:

A. High output power

B. Very high frequency stability

C. Tunability over a wide range

D. Low cost

Question 24

In a common-collector (emitter follower) amplifier:

A. Voltage gain is very high and output impedance is high

B. Voltage gain is slightly less than unity and output impedance is low

C. Current gain is less than one

D. The output is 180 degrees out of phase with the input

Question 25

A varactor (varicap) diode is used mainly as a:

A. Fixed capacitor

B. Voltage-controlled capacitance in tuning circuits

C. Voltage regulator

D. Rectifier at high frequencies

Questions

Section 1 - Electronic Devices and Circuits - Set 1