Diode dynamic resistance in forward bias is

 

121️⃣

Q: Avalanche breakdown occurs due to
Options:
A) Strong electric field causing tunneling
B) Collision of charge carriers
C) Thermal runaway
D) Doping concentration
Answer: B) Collision of charge carriers
Explanation:
In avalanche breakdown, energetic carriers collide with atoms, generating more carriers — leading to a chain reaction.

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122️⃣

Q: Zener breakdown occurs at
Options:
A) High reverse voltage
B) Low reverse voltage
C) Zero bias
D) Forward bias
Answer: B) Low reverse voltage
Explanation:
Zener breakdown happens in heavily doped diodes with a narrow depletion region at relatively low reverse voltages (<5V).

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123️⃣

Q: The breakdown voltage of a Zener diode decreases with
Options:
A) Increase in temperature
B) Decrease in temperature
C) Independent of temperature
D) Reverse current
Answer: A) Increase in temperature
Explanation:
Zener breakdown voltage has a negative temperature coefficient — it decreases as temperature rises.

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124️⃣

Q: The reverse current in a Zener diode beyond breakdown is
Options:
A) Constant
B) Increases exponentially
C) Decreases
D) Oscillates
Answer: A) Constant
Explanation:
In breakdown region, the Zener diode maintains nearly constant voltage; hence current change doesn’t affect voltage much.

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125️⃣

Q: The main use of a Zener diode is in
Options:
A) Rectifier circuits
B) Voltage regulation
C) Amplifier circuits
D) Oscillator circuits
Answer: B) Voltage regulation
Explanation:
Because it maintains a constant voltage across it in breakdown, it is ideal for voltage regulation applications.

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126️⃣

Q: The diode used in radio frequency tuning circuits is
Options:
A) Zener diode
B) Varactor diode
C) LED
D) Schottky diode
Answer: B) Varactor diode
Explanation:
The variable capacitance of varactor diodes helps in tuning RF circuits.

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127️⃣

Q: The forward bias voltage of a germanium diode is approximately
Options:
A) 0.1 V
B) 0.3 V
C) 0.5 V
D) 0.7 V
Answer: B) 0.3 V
Explanation:
Germanium diodes require about 0.3 V to start conducting due to lower barrier potential than silicon.

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128️⃣

Q: When a diode is forward biased, the barrier potential
Options:
A) Increases
B) Decreases
C) Remains constant
D) Becomes infinite
Answer: B) Decreases
Explanation:
Forward bias lowers the potential barrier, allowing more carriers to flow across the junction.

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129️⃣

Q: In a reverse-biased diode, the width of the depletion region
Options:
A) Decreases
B) Increases
C) Remains constant
D) Becomes zero
Answer: B) Increases
Explanation:
Reverse bias widens the depletion layer, further restricting majority carrier flow.

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130️⃣

Q: The most commonly used semiconductor material for diodes is
Options:
A) Germanium
B) Silicon
C) Gallium
D) Arsenic
Answer: B) Silicon
Explanation:
Silicon is preferred due to its thermal stability, low leakage, and availability.

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131️⃣

Q: The diode current equation is
Options:
A) $I = I_0 (e^{V/V_T} - 1)$
B) $I = V/I_0$
C) $I = I_0 (1 - e^{V/V_T})$
D) $I = V_T (e^{I/I_0})$
Answer: A) $I = I_0 (e^{V/V_T} - 1)$
Explanation:
This is the standard diode equation showing exponential rise of current with forward voltage.

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132️⃣

Q: Thermal voltage (Vₜ) at room temperature (300 K) is approximately
Options:
A) 0.1 V
B) 0.026 V
C) 1 V
D) 0.7 V
Answer: B) 0.026 V
Explanation:
At 300 K, $V_T = kT/q = 0.026 V$.

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133️⃣

Q: The term “knee voltage” refers to
Options:
A) Reverse voltage limit
B) Forward voltage where conduction begins
C) Breakdown voltage
D) Ripple voltage
Answer: B) Forward voltage where conduction begins
Explanation:
Knee voltage is the forward voltage beyond which the diode conducts heavily.

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134️⃣

Q: Diode clipping circuits are used for
Options:
A) Amplifying signals
B) Limiting signal amplitude
C) Rectification
D) Filtering
Answer: B) Limiting signal amplitude
Explanation:
Clipping circuits remove or “clip” portions of input signal above or below preset voltage levels.

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135️⃣

Q: In a clamper circuit, the diode is used to
Options:
A) Limit the signal
B) Shift DC level
C) Amplify signal
D) Invert signal
Answer: B) Shift DC level
Explanation:
Clampers add or subtract a DC level from an AC signal without changing shape.

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136️⃣

Q: The frequency response of a diode is limited due to
Options:
A) Capacitance effects
B) Inductive effects
C) Resistance
D) Leakage
Answer: A) Capacitance effects
Explanation:
Junction capacitance limits the diode’s performance at high frequencies.

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137️⃣

Q: The reverse recovery time of a fast recovery diode is typically
Options:
A) 1 μs
B) 100 ns
C) 10 ms
D) 1 s
Answer: B) 100 ns
Explanation:
Fast recovery diodes have short storage times (~100 ns) suitable for high-speed switching.

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138️⃣

Q: A photodiode is normally operated under
Options:
A) Forward bias
B) Reverse bias
C) Zero bias
D) AC bias
Answer: B) Reverse bias
Explanation:
Reverse bias widens the depletion layer, improving sensitivity to incident light.

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139️⃣

Q: Which of the following is not a diode?
Options:
A) Tunnel diode
B) Varactor diode
C) Gunn diode
D) Zener diode
Answer: C) Gunn diode
Explanation:
Gunn diodes operate on transferred-electron mechanism, not P–N junction principles.

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140️⃣

Q: The avalanche breakdown voltage increases if
Options:
A) Doping concentration decreases
B) Doping concentration increases
C) Temperature increases
D) Depletion width decreases
Answer: A) Doping concentration decreases
Explanation:
Light doping increases depletion width, requiring a higher voltage for avalanche breakdown.

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141️⃣

Q: The leakage current in a silicon diode is about
Options:
A) 100 μA
B) 1 μA
C) 1 nA
D) 1 A
Answer: C) 1 nA
Explanation:
Silicon diodes have extremely low reverse leakage, typically in nanoampere range.

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142️⃣

Q: The efficiency of a half-wave rectifier is
Options:
A) 40.6%
B) 81.2%
C) 50%
D) 90%
Answer: A) 40.6%
Explanation:
Theoretical maximum efficiency of half-wave rectifier is 40.6%.

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143️⃣

Q: For a full-wave bridge rectifier, the PIV per diode is
Options:
A) Vm
B) 2Vm
C) Vm/2
D) 4Vm
Answer: A) Vm
Explanation:
Each diode must withstand only one peak voltage in bridge rectifier configuration.

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144️⃣

Q: The average DC output voltage of a full-wave rectifier is
Options:
A) 0.318 Vm
B) 0.636 Vm
C) 0.707 Vm
D) 1.414 Vm
Answer: B) 0.636 Vm
Explanation:
Average output = $2Vm/π = 0.636Vm$.

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145️⃣

Q: In a rectifier circuit, increasing filter capacitance will
Options:
A) Increase ripple
B) Decrease ripple
C) No change
D) Reduce DC output
Answer: B) Decrease ripple
Explanation:
Larger capacitance stores more charge, reducing voltage variations (ripple).

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146️⃣

Q: The ripple frequency in a full-wave rectifier is
Options:
A) Same as input
B) Twice input
C) Half of input
D) None
Answer: B) Twice input
Explanation:
Two pulses of output per input AC cycle → ripple frequency = 2 × supply frequency.

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147️⃣

Q: Diode dynamic resistance in forward bias is
Options:
A) High
B) Low
C) Infinite
D) Negative
Answer: B) Low
Explanation:
Once conducting, diode shows very small resistance due to high current flow.

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148️⃣

Q: A silicon diode stops conducting when reverse bias exceeds
Options:
A) 0.7 V
B) 1 V
C) Breakdown voltage
D) Knee voltage
Answer: C) Breakdown voltage
Explanation:
Above breakdown, avalanche or Zener effect dominates, causing large current.

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149️⃣

Q: The cut-in voltage for a germanium diode is
Options:
A) 0.1 V
B) 0.3 V
C) 0.6 V
D) 1 V
Answer: B) 0.3 V
Explanation:
Also known as knee voltage, for Ge it’s around 0.3 V.

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150️⃣

Q: A diode acts as
Options:
A) Linear device
B) Non-linear device
C) Passive linear
D) Bilateral device
Answer: B) Non-linear device
Explanation:
Current–voltage relationship of diode is exponential, hence non-linear.