151️⃣
Q: The diode used in microwave oscillators is
Options:
A) Tunnel diode
B) Varactor diode
C) Schottky diode
D) Zener diode
Answer: A) Tunnel diode
Explanation:
Tunnel diodes exhibit negative resistance and are used in microwave oscillators and amplifiers.
152️⃣
Q: The negative resistance region in tunnel diode occurs due to
Options:
A) Avalanche effect
B) Tunneling of electrons
C) Impact ionization
D) Thermal runaway
Answer: B) Tunneling of electrons
Explanation:
At certain voltage levels, electrons tunnel through the potential barrier, leading to a decrease in current with increasing voltage.
153️⃣
Q: The symbol of LED has an arrow indicating
Options:
A) Current entering
B) Light emission
C) Reverse current
D) Power dissipation
Answer: B) Light emission
Explanation:
The arrows in the LED symbol point outward, representing emission of light from the junction.
154️⃣
Q: The efficiency of an LED is determined by
Options:
A) Forward resistance
B) Light output per input power
C) Voltage drop
D) Current gain
Answer: B) Light output per input power
Explanation:
Efficiency (η) = Optical power output / Electrical power input.
155️⃣
Q: The most commonly used material for visible LEDs is
Options:
A) Si
B) Ge
C) GaAsP
D) InSb
Answer: C) GaAsP
Explanation:
Gallium Arsenide Phosphide (GaAsP) produces red, yellow, or green light depending on composition.
156️⃣
Q: Photodiode sensitivity is expressed in
Options:
A) A/W (Ampere per Watt)
B) V/A (Volt per Ampere)
C) Ω (Ohm)
D) W/m²
Answer: A) A/W
Explanation:
Photodiode sensitivity indicates how much photocurrent is generated per unit optical power.
157️⃣
Q: The capacitance of a reverse-biased junction decreases when
Options:
A) Reverse bias decreases
B) Reverse bias increases
C) Frequency increases
D) None
Answer: B) Reverse bias increases
Explanation:
Wider depletion region with higher reverse bias reduces junction capacitance.
158️⃣
Q: Power diodes are usually constructed using
Options:
A) Metal–semiconductor junctions
B) P–I–N structure
C) N–P–N layers
D) P–P junction
Answer: B) P–I–N structure
Explanation:
P–I–N diodes handle large voltages and currents, as the intrinsic layer supports high reverse voltages.
159️⃣
Q: The reverse recovery time of power diodes is
Options:
A) Very small
B) Large (microseconds)
C) Zero
D) Instantaneous
Answer: B) Large (microseconds)
Explanation:
Power diodes have longer recovery time (~μs) due to high stored charge.
160️⃣
Q: The voltage drop across a conducting silicon power diode is about
Options:
A) 0.3 V
B) 0.7 V
C) 1.0 V
D) 2.0 V
Answer: C) 1.0 V
Explanation:
Power diodes have larger junction area, resulting in slightly higher forward drop (~1 V).
161️⃣
Q: A Schottky diode is preferred in switching circuits because
Options:
A) High breakdown voltage
B) Fast recovery
C) High forward resistance
D) High power capacity
Answer: B) Fast recovery
Explanation:
Schottky diodes have no minority carrier storage, leading to fast switching.
162️⃣
Q: The reverse leakage current of a Schottky diode is
Options:
A) Higher than PN diode
B) Lower than PN diode
C) Same as PN diode
D) Zero
Answer: A) Higher than PN diode
Explanation:
Metal–semiconductor junction has more leakage current than PN junction due to majority carrier conduction.
163️⃣
Q: In forward bias, the diode current is mainly due to
Options:
A) Drift of electrons
B) Diffusion of charge carriers
C) Recombination
D) Tunneling
Answer: B) Diffusion of charge carriers
Explanation:
Forward bias reduces barrier potential, allowing carriers to diffuse across the junction.
164️⃣
Q: Reverse bias current in diode is due to
Options:
A) Majority carriers
B) Minority carriers
C) Both
D) None
Answer: B) Minority carriers
Explanation:
Minority carriers cross the junction in reverse bias causing small leakage current.
165️⃣
Q: The unit of reverse recovery time is
Options:
A) Second
B) Millisecond
C) Microsecond or nanosecond
D) None
Answer: C) Microsecond or nanosecond
Explanation:
It’s measured in μs or ns depending on diode type.
166️⃣
Q: A diode that emits light when forward biased is called
Options:
A) Varactor diode
B) LED
C) Zener diode
D) Photodiode
Answer: B) LED
Explanation:
LEDs emit photons during electron–hole recombination.
167️⃣
Q: The main loss in a diode rectifier circuit is
Options:
A) Copper loss
B) Iron loss
C) Forward voltage drop loss
D) Core loss
Answer: C) Forward voltage drop loss
Explanation:
Energy is lost as heat due to the forward voltage drop across diode.
168️⃣
Q: In a diode, reverse saturation current is
Options:
A) Constant for all voltages
B) Increases with temperature
C) Decreases with forward bias
D) Zero
Answer: B) Increases with temperature
Explanation:
More thermal generation of carriers increases exponentially with temperature.
169️⃣
Q: When a diode is reverse biased, the current is of the order of
Options:
A) Ampere
B) Milliampere
C) Microampere or less
D) None
Answer: C) Microampere or less
Explanation:
Reverse current is very small due to minority carriers.
170️⃣
Q: The diode that can be used as a microwave frequency multiplier is
Options:
A) Tunnel diode
B) Varactor diode
C) Zener diode
D) LED
Answer: B) Varactor diode
Explanation:
Due to voltage-dependent capacitance, varactor diodes generate harmonics for frequency multiplication.
171️⃣
Q: The process of converting AC into DC is called
Options:
A) Regulation
B) Rectification
C) Amplification
D) Modulation
Answer: B) Rectification
Explanation:
Diodes are used to convert alternating current to direct current through rectification.
172️⃣
Q: The bridge rectifier requires how many diodes?
Options:
A) 1
B) 2
C) 4
D) 6
Answer: C) 4
Explanation:
A bridge rectifier uses 4 diodes to convert AC into full-wave DC.
173️⃣
Q: The efficiency of bridge rectifier is
Options:
A) 40.6%
B) 50%
C) 81.2%
D) 90%
Answer: C) 81.2%
Explanation:
Same as center-tap full-wave rectifier, theoretical efficiency = 81.2%.
174️⃣
Q: The output frequency of a full-wave rectifier for 50 Hz AC input is
Options:
A) 25 Hz
B) 50 Hz
C) 100 Hz
D) 150 Hz
Answer: C) 100 Hz
Explanation:
Output contains two pulses per input cycle → frequency = 2 × input = 100 Hz.
175️⃣
Q: The diode used for voltage regulation has
Options:
A) Negative resistance region
B) Constant voltage region
C) Variable capacitance
D) Photo sensitivity
Answer: B) Constant voltage region
Explanation:
Zener diode maintains constant voltage beyond its breakdown point.
176️⃣
Q: The temperature coefficient of a Zener diode is
Options:
A) Positive
B) Negative
C) Zero
D) Infinite
Answer: B) Negative
Explanation:
Zener voltage decreases slightly with rise in temperature.
177️⃣
Q: A forward biased diode conducts current due to
Options:
A) Minority carriers
B) Majority carriers
C) Both
D) None
Answer: B) Majority carriers
Explanation:
Forward bias reduces the barrier, allowing majority carriers to flow easily.
178️⃣
Q: The static resistance of a diode is
Options:
A) V/I
B) I/V
C) dV/dI
D) dI/dV
Answer: A) V/I
Explanation:
Static or DC resistance is the ratio of voltage to current at a point on the I–V curve.
179️⃣
Q: For a silicon diode, the reverse saturation current doubles for every rise of
Options:
A) 1°C
B) 5°C
C) 10°C
D) 20°C
Answer: C) 10°C
Explanation:
roughly doubles for every 10°C increase in temperature.
180️⃣
Q: The diode used to detect amplitude modulated signals is
Options:
A) Zener diode
B) Detector diode
C) Tunnel diode
D) Varactor diode
Answer: B) Detector diode
Explanation:
Detector (or demodulator) diode rectifies and filters AM signals.
181️⃣
Q: The turn-on voltage of a silicon diode is
Options:
A) 0.3 V
B) 0.5 V
C) 0.7 V
D) 1.0 V
Answer: C) 0.7 V
Explanation:
Typical knee voltage of Si diode is about 0.7 V.
182️⃣
Q: Which diode operates on quantum mechanical tunneling?
Options:
A) Zener
B) Varactor
C) Tunnel
D) Schottky
Answer: C) Tunnel
Explanation:
Tunnel diode allows carriers to pass through potential barrier via tunneling effect.
183️⃣
Q: A photodiode generates current when
Options:
A) Forward biased
B) Reverse biased and exposed to light
C) Reverse biased in dark
D) Unbiased
Answer: B) Reverse biased and exposed to light
Explanation:
Incident photons create electron-hole pairs, producing photocurrent under reverse bias.
184️⃣
Q: The color of light from an LED depends on
Options:
A) Current magnitude
B) Forward voltage
C) Bandgap energy
D) Temperature
Answer: C) Bandgap energy
Explanation:
Photon energy = Bandgap energy → determines color (wavelength).
185️⃣
Q: The diode used as a voltage-controlled capacitor is
Options:
A) Schottky
B) Varactor
C) Tunnel
D) LED
Answer: B) Varactor
Explanation:
In reverse bias, depletion width varies → capacitance changes with voltage.
186️⃣
Q: The current through a forward-biased diode increases with
Options:
A) Reverse voltage
B) Forward voltage
C) Reverse resistance
D) Frequency
Answer: B) Forward voltage
Explanation:
As forward voltage rises, the exponential current relation increases sharply.
187️⃣
Q: The diode used for waveform shaping is
Options:
A) Tunnel
B) Zener
C) Clipping diode
D) LED
Answer: C) Clipping diode
Explanation:
Clipping diodes limit signal amplitude, shaping waveform peaks.
188️⃣
Q: When AC is applied to a half-wave rectifier, output is
Options:
A) Pure DC
B) Pulsating DC
C) AC
D) Constant
Answer: B) Pulsating DC
Explanation:
Only positive half-cycles are passed, producing pulsating DC.
189️⃣
Q: The diode acts as a short circuit when
Options:
A) Reverse biased
B) Forward biased
C) Unbiased
D) At breakdown
Answer: B) Forward biased
Explanation:
Forward bias reduces resistance; diode behaves like a short path for current.
190️⃣
Q: The main function of diode in a rectifier circuit is
Options:
A) Amplification
B) Rectification
C) Modulation
D) Stabilization
Answer: B) Rectification
Explanation:
It converts alternating current to direct current by allowing current in one direction.
191️⃣
Q: The current in a diode before knee voltage is
Options:
A) Very high
B) Very low
C) Constant
D) Infinite
Answer: B) Very low
Explanation:
Before knee voltage, barrier potential prevents significant current flow.
192️⃣
Q: The forward characteristic of a diode is
Options:
A) Linear
B) Exponential
C) Constant
D) Parabolic
Answer: B) Exponential
Explanation:
Follows exponential law .
193️⃣
Q: The resistance of a reverse-biased diode is
Options:
A) Very high
B) Very low
C) Zero
D) Negative
Answer: A) Very high
Explanation:
Almost no current flows in reverse bias, so resistance is very high.
194️⃣
Q: The forward current in a diode is limited by
Options:
A) Barrier potential
B) External resistor
C) Reverse leakage
D) Temperature
Answer: B) External resistor
Explanation:
Series resistor limits current to prevent diode damage in forward bias.
195️⃣
Q: The barrier potential for Si and Ge diodes are approximately
Options:
A) 0.7 V and 0.3 V
B) 0.3 V and 0.7 V
C) Both 0.7 V
D) Both 0.3 V
Answer: A) 0.7 V and 0.3 V
Explanation:
Typical barrier potentials are 0.7 V (Si) and 0.3 V (Ge).
196️⃣
Q: The diode that operates in reverse breakdown without damage is
Options:
A) Zener diode
B) Schottky diode
C) Varactor diode
D) LED
Answer: A) Zener diode
Explanation:
Zener diodes are designed to safely operate in breakdown region.
197️⃣
Q: The P–N junction is formed by
Options:
A) Joining two metals
B) Joining P-type and N-type materials
C) Doping a metal
D) Electroplating
Answer: B) Joining P-type and N-type materials
Explanation:
A P–N junction forms when P-type and N-type semiconductors are fused.
198️⃣
Q: The depletion region contains
Options:
A) Only free electrons
B) Only holes
C) Immobile ions
D) Neutral atoms
Answer: C) Immobile ions
Explanation:
Fixed positive and negative ions remain after diffusion, forming the depletion region.
199️⃣
Q: A diode can be destroyed if
Options:
A) Reverse bias exceeds breakdown
B) Forward current exceeds limit
C) Reverse current exceeds limit
D) Both B and C
Answer: D) Both B and C
Explanation:
Excess forward or reverse current can overheat and damage the diode junction.
200️⃣
Q: In a rectifier circuit, the DC output is improved using
Options:
A) Transformer
B) Filter capacitor
C) Inductor only
D) Switch
Answer: B) Filter capacitor
Explanation:
A capacitor filter smooths the pulsating DC to produce steadier output voltage.
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