451️⃣
Q: The efficiency of an LED is defined as
Options:
A) Ratio of electrical to optical power
B) Ratio of optical to electrical power
C) Ratio of luminous flux to current
D) Ratio of voltage to current
Answer: B) Ratio of optical to electrical power
Explanation:
Efficiency (η) = Output optical power / Input electrical power.
452️⃣
Q: A laser diode emits
Options:
A) Coherent light
B) Incoherent light
C) Diffused light
D) Polarized light only
Answer: A) Coherent light
Explanation:
Laser diodes produce light waves that are coherent and monochromatic.
453️⃣
Q: The optical output power of a laser diode increases
Options:
A) Linearly with current beyond threshold
B) Exponentially with voltage
C) Inversely with current
D) Constantly with voltage
Answer: A) Linearly with current beyond threshold
Explanation:
Once threshold current is reached, further current increases output almost linearly.
454️⃣
Q: The threshold current in a laser diode is
Options:
A) Minimum current for lasing action
B) Reverse leakage current
C) Forward current for LED emission
D) Zero current
Answer: A) Minimum current for lasing action
Explanation:
It is the smallest current required to achieve population inversion and light amplification.
455️⃣
Q: The output wavelength of a laser diode is determined by
Options:
A) Bias voltage
B) Active region material
C) Frequency of input current
D) Ambient light
Answer: B) Active region material
Explanation:
The bandgap of the semiconductor determines the emission wavelength.
456️⃣
Q: Photodiodes convert
Options:
A) Voltage to light
B) Light to current
C) Current to voltage
D) Light to heat
Answer: B) Light to current
Explanation:
Incident photons generate electron-hole pairs, producing photocurrent.
457️⃣
Q: The output of a photodiode is
Options:
A) Current
B) Voltage
C) Power
D) Resistance
Answer: A) Current
Explanation:
Photodiodes generate a current proportional to the light intensity.
458️⃣
Q: A photodiode is used in which type of mode for high-speed detection?
Options:
A) Photovoltaic mode
B) Photoconductive mode
C) Forward bias mode
D) Saturation mode
Answer: B) Photoconductive mode
Explanation:
Reverse biasing (photoconductive mode) reduces junction capacitance and allows faster response.
459️⃣
Q: The response time of a photodiode depends on
Options:
A) Junction capacitance
B) Depletion width
C) Reverse bias voltage
D) All of these
Answer: D) All of these
Explanation:
Higher reverse bias widens depletion region and reduces capacitance → faster response.
460️⃣
Q: The dark current in a photodiode is
Options:
A) Zero
B) Current when no light falls
C) Maximum current
D) Proportional to light
Answer: B) Current when no light falls
Explanation:
Even in complete darkness, a small reverse leakage called dark current exists.
461️⃣
Q: The junction capacitance of a diode
Options:
A) Increases with reverse voltage
B) Decreases with reverse voltage
C) Remains constant
D) Independent of bias
Answer: B) Decreases with reverse voltage
Explanation:
Higher reverse bias widens depletion layer, reducing capacitance.
462️⃣
Q: The temperature coefficient of a silicon diode forward voltage is approximately
Options:
A) +2 mV/°C
B) –2 mV/°C
C) Zero
D) +0.7 mV/°C
Answer: B) –2 mV/°C
Explanation:
Forward voltage drop decreases roughly by 2 mV for every 1°C rise.
463️⃣
Q: Power diodes are designed for
Options:
A) Low voltage, high current
B) High voltage, high current
C) Low power circuits
D) High-frequency signals
Answer: B) High voltage, high current
Explanation:
Power diodes handle large voltages and currents for rectification in power supplies.
464️⃣
Q: The reverse recovery time of a power diode is
Options:
A) Negligible
B) Higher than small-signal diode
C) Same as Schottky
D) Independent of doping
Answer: B) Higher than small-signal diode
Explanation:
Due to large junction area and stored charge, recovery time is longer.
465️⃣
Q: The average forward current rating of a diode depends on
Options:
A) Junction temperature
B) Material type
C) Forward resistance
D) All of these
Answer: D) All of these
Explanation:
Thermal and electrical properties together determine safe current handling.
466️⃣
Q: The peak repetitive reverse voltage (PRV) rating defines
Options:
A) Forward voltage drop
B) Maximum allowable reverse voltage
C) Average rectified voltage
D) RMS voltage
Answer: B) Maximum allowable reverse voltage
Explanation:
PRV is the maximum voltage a diode can withstand repeatedly in reverse bias without breakdown.
467️⃣
Q: Fast recovery diodes are used in
Options:
A) High-frequency rectifiers
B) Low-frequency circuits
C) DC filters
D) Heaters
Answer: A) High-frequency rectifiers
Explanation:
They have short reverse recovery times, making them ideal for switching circuits.
468️⃣
Q: A diode acts as a short circuit when
Options:
A) Forward biased
B) Reverse biased
C) No bias
D) Under breakdown
Answer: A) Forward biased
Explanation:
Forward-biased diode offers very low resistance.
469️⃣
Q: Avalanche diodes are used in
Options:
A) Voltage regulation
B) High-speed switching
C) Noise generation
D) All of these
Answer: D) All of these
Explanation:
Avalanche diodes are used for high-speed switching, voltage references, and RF noise sources.
470️⃣
Q: Tunnel diodes are used in
Options:
A) Oscillators
B) Amplifiers
C) Mixers
D) All of these
Answer: D) All of these
Explanation:
Negative resistance characteristic enables use in oscillators, amplifiers, and high-speed circuits.
471️⃣
Q: The main reason for negative resistance in tunnel diode is
Options:
A) Quantum tunneling
B) Avalanche effect
C) High doping
D) Reverse bias
Answer: A) Quantum tunneling
Explanation:
Extremely heavy doping allows tunneling through a narrow potential barrier.
472️⃣
Q: In tunnel diode, the peak current depends on
Options:
A) Doping concentration
B) Junction area
C) Temperature
D) All
Answer: D) All
Explanation:
All these parameters influence tunneling probability and hence the peak current.
473️⃣
Q: A diode used for microwave frequency detection is
Options:
A) PIN diode
B) Tunnel diode
C) Gunn diode
D) Varactor diode
Answer: C) Gunn diode
Explanation:
Gunn diodes exhibit negative differential resistance used in microwave oscillators.
474️⃣
Q: The Gunn diode is made from
Options:
A) GaAs or InP
B) Si
C) Ge
D) GaN
Answer: A) GaAs or InP
Explanation:
Gunn diodes use materials like Gallium Arsenide that exhibit transferred electron effect.
475️⃣
Q: The transferred electron effect is observed in
Options:
A) Schottky diode
B) Gunn diode
C) PIN diode
D) Zener diode
Answer: B) Gunn diode
Explanation:
The effect causes negative resistance, leading to microwave oscillations.
476️⃣
Q: Temperature rise in a diode affects
Options:
A) Barrier potential
B) Leakage current
C) Efficiency
D) All of these
Answer: D) All of these
Explanation:
Increasing temperature reduces barrier potential, increases leakage, and may reduce efficiency.
477️⃣
Q: The main function of a flyback diode in inductive load circuits is
Options:
A) Boost voltage
B) Protect switch from voltage spikes
C) Increase current
D) Stabilize frequency
Answer: B) Protect switch from voltage spikes
Explanation:
Flyback (freewheeling) diode provides a path for inductive current to prevent voltage spikes.
478️⃣
Q: A diode used to limit voltage surges is
Options:
A) Zener diode
B) TVS diode
C) Schottky diode
D) LED
Answer: B) TVS diode
Explanation:
Transient Voltage Suppression diodes clamp high-voltage transients.
479️⃣
Q: The symbol of Zener diode differs from PN diode in
Options:
A) Number of terminals
B) Shape of cathode line
C) Direction of arrow
D) None
Answer: B) Shape of cathode line
Explanation:
Zener diode symbol has a bent line at cathode to indicate breakdown behavior.
480️⃣
Q: The cut-in voltage for a silicon diode is
Options:
A) 0.3 V
B) 0.5 V
C) 0.7 V
D) 1 V
Answer: C) 0.7 V
Explanation:
A silicon diode typically starts conducting around 0.7 volts forward bias.
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