201️⃣
Q: The voltage across a conducting LED typically lies between
Options:
A) 0.3 – 0.5 V
B) 0.7 – 1.2 V
C) 1.5 – 3.5 V
D) 4 – 6 V
Answer: C) 1.5 – 3.5 V
Explanation:
The voltage drop depends on color (bandgap). Red LEDs ≈ 1.8 V, blue ≈ 3.3 V.
202️⃣
Q: A varactor diode works on the principle of
Options:
A) Avalanche breakdown
B) Junction capacitance variation
C) Negative resistance
D) Light emission
Answer: B) Junction capacitance variation
Explanation:
In reverse bias, depletion width changes with voltage, altering junction capacitance.
203️⃣
Q: A photodiode operates effectively when it is
Options:
A) Forward biased
B) Reverse biased
C) Unbiased
D) Forward and illuminated
Answer: B) Reverse biased
Explanation:
Reverse bias widens the depletion region for better light response and faster operation.
204️⃣
Q: In a photodiode, if the intensity of light increases, the photocurrent
Options:
A) Decreases
B) Increases
C) Remains constant
D) Becomes zero
Answer: B) Increases
Explanation:
More photons → more electron–hole pairs → higher photocurrent.
205️⃣
Q: The diode used in tuning circuits of RF receivers is
Options:
A) Tunnel diode
B) Varactor diode
C) Zener diode
D) LED
Answer: B) Varactor diode
Explanation:
Varactor acts as a voltage-controlled capacitor in tuning and frequency modulation circuits.
206️⃣
Q: The negative resistance region of a tunnel diode lies between
Options:
A) 0 V – 0.1 V
B) Peak and valley points
C) Breakdown and saturation
D) Reverse bias region
Answer: B) Peak and valley points
Explanation:
Between these points, diode current decreases with increasing voltage — negative resistance region.
207️⃣
Q: Schottky diodes are preferred in digital circuits because of
Options:
A) Low cost
B) Low forward voltage and fast switching
C) High power handling
D) Thermal stability
Answer: B) Low forward voltage and fast switching
Explanation:
Schottky diodes drop only 0.3 – 0.4 V and switch in nanoseconds.
208️⃣
Q: The reverse recovery time of a Schottky diode is approximately
Options:
A) Several microseconds
B) A few nanoseconds
C) Milliseconds
D) Seconds
Answer: B) A few nanoseconds
Explanation:
Since it has no minority carrier storage, recovery is extremely fast (ns range).
209️⃣
Q: The reverse breakdown voltage of a Zener diode depends on
Options:
A) Doping concentration
B) Junction area
C) Temperature
D) All of the above
Answer: D) All of the above
Explanation:
Zener voltage varies with doping, junction size, and temperature.
210️⃣
Q: Zener diodes are fabricated for voltages up to
Options:
A) 3 V
B) 15 V
C) 200 V
D) 1000 V
Answer: C) 200 V
Explanation:
Zeners are commonly available from 2 V to about 200 V.
211️⃣
Q: The temperature coefficient of a 5.6 V Zener diode is
Options:
A) Positive
B) Negative
C) Nearly zero
D) Very high
Answer: C) Nearly zero
Explanation:
At ~5.6 V, temperature effects of Zener and avalanche mechanisms cancel out.
212️⃣
Q: A Zener diode is connected in a circuit for
Options:
A) Frequency modulation
B) Voltage regulation
C) Signal amplification
D) Phase shifting
Answer: B) Voltage regulation
Explanation:
Zeners maintain nearly constant output voltage despite supply or load changes.
213️⃣
Q: The region where the Zener diode maintains constant voltage is called
Options:
A) Forward bias region
B) Reverse saturation region
C) Breakdown region
D) Avalanche region only
Answer: C) Breakdown region
Explanation:
Voltage remains constant in breakdown region due to Zener effect.
214️⃣
Q: The capacitance of a varactor diode is
Options:
A) Constant
B) Inversely proportional to reverse voltage
C) Directly proportional to reverse voltage
D) Independent of voltage
Answer: B) Inversely proportional to reverse voltage
Explanation:
As reverse voltage increases, depletion width increases → capacitance decreases.
215️⃣
Q: The reverse current of a photodiode in darkness is known as
Options:
A) Photocurrent
B) Dark current
C) Leakage current
D) Bias current
Answer: B) Dark current
Explanation:
Small reverse current flows even without illumination — dark current.
216️⃣
Q: Which diode is most suitable for high-frequency applications?
Options:
A) P–N junction diode
B) Tunnel diode
C) Schottky diode
D) Zener diode
Answer: C) Schottky diode
Explanation:
Schottky diodes switch extremely fast, suitable for GHz range.
217️⃣
Q: The main reason for fast switching in Schottky diode is
Options:
A) Metal contact
B) No minority carrier charge storage
C) High barrier potential
D) Low doping
Answer: B) No minority carrier charge storage
Explanation:
Only majority carriers involved — no charge storage delay.
218️⃣
Q: The device used as a variable capacitor is
Options:
A) Tunnel diode
B) Varactor diode
C) Schottky diode
D) Zener diode
Answer: B) Varactor diode
Explanation:
Varactor changes capacitance with applied reverse voltage.
219️⃣
Q: The reverse voltage at which avalanche breakdown occurs in a Zener diode depends on
Options:
A) Doping level
B) Temperature
C) Both A and B
D) None
Answer: C) Both A and B
Explanation:
Heavily doped → Zener effect; lightly doped → avalanche effect; both affected by temperature.
220️⃣
Q: The light output of an LED increases with
Options:
A) Reverse current
B) Forward current
C) Temperature only
D) Reverse bias
Answer: B) Forward current
Explanation:
More forward current → more electron-hole recombination → more photons.
221️⃣
Q: The material commonly used for infrared LEDs is
Options:
A) GaAs
B) GaP
C) SiC
D) ZnS
Answer: A) GaAs
Explanation:
Gallium Arsenide emits infrared light.
222️⃣
Q: The photodiode is operated under
Options:
A) Forward bias
B) Reverse bias
C) No bias
D) Both
Answer: B) Reverse bias
Explanation:
Reverse bias enhances speed and sensitivity by widening depletion region.
223️⃣
Q: The major difference between LED and photodiode is
Options:
A) Material used
B) Direction of current flow and energy conversion
C) Both emit light
D) Both absorb light
Answer: B) Direction of current flow and energy conversion
Explanation:
LED converts electrical energy to light; photodiode converts light to electrical energy.
224️⃣
Q: The symbol of a photodiode shows arrows
Options:
A) Pointing outward
B) Pointing inward
C) One inward, one outward
D) None
Answer: B) Pointing inward
Explanation:
Arrows indicate light entering the device.
225️⃣
Q: The resistance of a forward-biased diode is
Options:
A) Very high
B) Very low
C) Infinite
D) Variable
Answer: B) Very low
Explanation:
Barrier potential is overcome, allowing high current flow → low resistance.
226️⃣
Q: The Zener effect dominates in diodes with breakdown voltage
Options:
A) > 6 V
B) < 5 V
C) Around 10 V
D) None
Answer: B) < 5 V
Explanation:
At low voltages (heavily doped junctions), tunneling/Zener effect dominates.
227️⃣
Q: Avalanche effect dominates in diodes with breakdown voltage
Options:
A) Less than 5 V
B) Greater than 6 V
C) Between 3 – 5 V
D) None
Answer: B) Greater than 6 V
Explanation:
Lightly doped junctions → higher breakdown → avalanche effect.
228️⃣
Q: A Zener diode is properly biased when
Options:
A) Reverse biased beyond breakdown
B) Forward biased
C) Reverse biased below breakdown
D) Zero bias
Answer: A) Reverse biased beyond breakdown
Explanation:
In breakdown, Zener maintains constant voltage.
229️⃣
Q: The output of a Zener regulator remains constant if
Options:
A) Load resistance decreases
B) Supply voltage varies
C) Both A and B (within limits)
D) None
Answer: C) Both A and B (within limits)
Explanation:
Zener regulator compensates small load or supply variations.
230️⃣
Q: The Zener current should always be
Options:
A) Zero
B) Above minimum and below maximum rated value
C) Equal to load current
D) Infinite
Answer: B) Above minimum and below maximum rated value
Explanation:
To maintain regulation, current must stay within specified range.
231️⃣
Q: Which diode can amplify microwave signals?
Options:
A) Schottky
B) Gunn
C) Tunnel
D) Varactor
Answer: C) Tunnel
Explanation:
Tunnel diodes use negative resistance to amplify at microwave frequencies.
232️⃣
Q: The storage and transition time in a diode affect
Options:
A) Reverse current
B) Switching speed
C) Power dissipation
D) Barrier potential
Answer: B) Switching speed
Explanation:
They define how fast a diode can switch between states.
233️⃣
Q: The diode that converts light directly into electrical energy is
Options:
A) LED
B) Photodiode
C) Solar cell
D) Varactor
Answer: C) Solar cell
Explanation:
Solar cells are large-area photodiodes optimized for power generation.
234️⃣
Q: The typical open-circuit voltage of a silicon solar cell is about
Options:
A) 0.3 V
B) 0.45 – 0.6 V
C) 0.9 V
D) 1.2 V
Answer: B) 0.45 – 0.6 V
Explanation:
Each Si solar cell produces ~0.5 V under standard illumination.
235️⃣
Q: Photodiodes have
Options:
A) High capacitance
B) Low capacitance and fast response
C) High current gain
D) Large forward voltage
Answer: B) Low capacitance and fast response
Explanation:
Reverse bias minimizes capacitance and improves speed.
236️⃣
Q: The depletion region of a heavily doped diode is
Options:
A) Wide
B) Narrow
C) Infinite
D) Constant
Answer: B) Narrow
Explanation:
Heavier doping → more charge carriers → smaller depletion width.
237️⃣
Q: In reverse bias, the electric field across the junction
Options:
A) Aids majority carriers
B) Opposes majority carriers
C) Aids minority carriers
D) Has no effect
Answer: B) Opposes majority carriers
Explanation:
Reverse voltage widens depletion region, preventing majority flow.
238️⃣
Q: A diode can be used as
Options:
A) Switch
B) Rectifier
C) Protection device
D) All of the above
Answer: D) All of the above
Explanation:
Diodes are used for rectification, switching, and protection from reverse polarity.
239️⃣
Q: The diode used for RF detection is
Options:
A) Zener
B) Schottky
C) Varactor
D) LED
Answer: B) Schottky
Explanation:
Low forward drop and fast switching make it ideal for RF detection.
240️⃣
Q: The ideal diode has
Options:
A) Zero resistance in forward bias, infinite in reverse bias
B) Infinite resistance in forward bias
C) Same resistance both ways
D) Finite resistance both ways
Answer: A) Zero resistance in forward bias, infinite in reverse bias
Explanation:
An ideal diode conducts perfectly one way, blocks perfectly the other.
241️⃣
Q: In forward bias, the barrier potential
Options:
A) Increases
B) Decreases
C) Remains constant
D) Becomes zero
Answer: B) Decreases
Explanation:
Applied voltage reduces barrier potential, allowing current flow.
242️⃣
Q: The diode used in reverse polarity protection of circuits is
Options:
A) Zener
B) Series diode
C) Schottky
D) Tunnel
Answer: B) Series diode
Explanation:
A forward-biased series diode blocks reverse current if polarity is wrong.
243️⃣
Q: The process by which diode converts AC to DC is
Options:
A) Clipping
B) Clamping
C) Rectification
D) Modulation
Answer: C) Rectification
Explanation:
Rectifiers allow current in one direction, converting AC → DC.
244️⃣
Q: The diode used in voltage doubler circuits is
Options:
A) Tunnel
B) Zener
C) Ordinary rectifier
D) Varactor
Answer: C) Ordinary rectifier
Explanation:
Simple PN diodes are used in voltage multiplier circuits.
245️⃣
Q: When temperature increases, the barrier potential
Options:
A) Increases
B) Decreases
C) Constant
D) Independent
Answer: B) Decreases
Explanation:
Barrier potential falls ~2 mV/°C for silicon diodes.
246️⃣
Q: The diode used to protect circuits from voltage spikes is
Options:
A) Schottky
B) Varistor
C) Zener
D) TVS diode
Answer: D) TVS diode
Explanation:
Transient Voltage Suppression (TVS) diodes clamp high-voltage transients safely.
247️⃣
Q: The maximum reverse voltage a diode can withstand is called
Options:
A) Reverse saturation voltage
B) Peak inverse voltage (PIV)
C) Barrier potential
D) Reverse recovery voltage
Answer: B) Peak inverse voltage (PIV)
Explanation:
PIV is the maximum voltage diode can tolerate in reverse before breakdown.
248️⃣
Q: The forward current of a diode increases exponentially because
Options:
A) Barrier potential remains constant
B) Diffusion current increases exponentially
C) Mobility increases
D) Depletion region widens
Answer: B) Diffusion current increases exponentially
Explanation:
Forward bias reduces barrier → exponential increase in diffusion current.
249️⃣
Q: The region responsible for diode rectifying property is
Options:
A) Depletion region
B) P-region
C) N-region
D) Contact terminals
Answer: A) Depletion region
Explanation:
The depletion region acts as a potential barrier allowing unidirectional conduction.
250️⃣
Q: Reverse saturation current in a diode depends mainly on
Options:
A) Doping concentration and temperature
B) Frequency
C) Forward bias
D) Load resistance
Answer: A) Doping concentration and temperature
Explanation:
Higher temperature or lower doping increases reverse saturation current.
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