11️⃣
Q: The main function of a diode in an electronic circuit is
Options:
A) To amplify signal
B) To control current direction
C) To generate AC
D) To produce noise
Answer: B) To control current direction
Explanation:
A diode allows current in one direction only and blocks in the reverse direction — acting as a one-way valve for current.
12️⃣
Q: The barrier potential of a germanium diode is approximately
Options:
A) 0.1 V
B) 0.2 V
C) 0.3 V
D) 0.7 V
Answer: C) 0.3 V
Explanation:
Germanium diodes require about 0.3 V to conduct in the forward direction.
13️⃣
Q: A diode is said to be forward-biased when
Options:
A) P-side connected to negative terminal
B) N-side connected to positive terminal
C) P-side connected to positive terminal
D) None of these
Answer: C) P-side connected to positive terminal
Explanation:
Forward bias means applying positive voltage to the P-side and negative to the N-side.
14️⃣
Q: In reverse bias, the depletion layer width
Options:
A) Decreases
B) Increases
C) Remains same
D) None
Answer: B) Increases
Explanation:
Reverse bias pulls majority carriers away from the junction, increasing the depletion width.
15️⃣
Q: The dynamic resistance of a diode is
Options:
A) Resistance offered to DC
B) Constant
C) Resistance offered to small signal AC
D) Infinite
Answer: C) Resistance offered to small signal AC
Explanation:
Dynamic resistance is the slope of the I–V curve at a point — it shows how current changes with a small change in voltage.
16️⃣
Q: When a diode is reverse biased and voltage is increased, the diode eventually
Options:
A) Breaks down
B) Short circuits
C) Heats up only
D) Acts as an open circuit
Answer: A) Breaks down
Explanation:
Beyond a certain voltage (breakdown voltage), the diode conducts heavily due to avalanche or Zener breakdown.
17️⃣
Q: The current in a reverse-biased diode is called
Options:
A) Reverse saturation current
B) Reverse conduction current
C) Minority current
D) Leakage current
Answer: A) Reverse saturation current
Explanation:
This small current due to minority carriers is called reverse saturation current, symbolized as .
18️⃣
Q: The temperature dependence of reverse saturation current is
Options:
A) Decreases with temperature
B) Doubles for every 10°C rise
C) Remains constant
D) Independent of temperature
Answer: B) Doubles for every 10°C rise
Explanation:
As temperature increases, more carriers are thermally generated, increasing approximately doubling every 10°C.
19️⃣
Q: The cut-in voltage of a silicon diode is approximately
Options:
A) 0.2 V
B) 0.3 V
C) 0.7 V
D) 1 V
Answer: C) 0.7 V
Explanation:
This is the threshold voltage required for conduction to start in silicon diodes.
20️⃣
Q: In a half-wave rectifier, the diode conducts for
Options:
A) Full cycle
B) Half cycle
C) Twice per cycle
D) None
Answer: B) Half cycle
Explanation:
In a half-wave rectifier, the diode conducts during the positive half cycle only.
21️⃣
Q: The efficiency of a half-wave rectifier is approximately
Options:
A) 10%
B) 20%
C) 40.6%
D) 81.2%
Answer: C) 40.6%
Explanation:
The maximum theoretical efficiency of a half-wave rectifier is 40.6%.
22️⃣
Q: The peak inverse voltage (PIV) of a diode in a half-wave rectifier is equal to
Options:
A) Vmax/2
B) Vmax
C) 2Vmax
D) Zero
Answer: B) Vmax
Explanation:
During reverse bias, the diode must withstand the full peak secondary voltage (Vmax).
23️⃣
Q: The PIV of a diode in a full-wave center-tap rectifier is
Options:
A) Vmax
B) 2Vmax
C) Vmax/2
D) None
Answer: B) 2Vmax
Explanation:
Each diode in a center-tapped rectifier must block twice the peak voltage.
24️⃣
Q: The ripple frequency in a full-wave rectifier is
Options:
A) Same as AC input
B) Double of input frequency
C) Half of input frequency
D) None
Answer: B) Double of input frequency
Explanation:
Both halves of AC input are used; hence output pulsates twice per cycle.
25️⃣
Q: A diode in forward bias shows current due to
Options:
A) Only electrons
B) Only holes
C) Both electrons and holes
D) None
Answer: C) Both electrons and holes
Explanation:
In a p–n junction, both electrons (from N) and holes (from P) contribute to forward current.
26️⃣
Q: The forward current increases exponentially with voltage because
Options:
A) Ohm’s law applies
B) The barrier potential reduces
C) Minority carriers increase
D) Doping increases
Answer: B) The barrier potential reduces
Explanation:
As forward bias increases, the barrier reduces exponentially, allowing more carriers to cross the junction.
27️⃣
Q: A diode connected across a relay coil is used for
Options:
A) Rectification
B) Protection from back EMF
C) Amplification
D) Signal modulation
Answer: B) Protection from back EMF
Explanation:
When the relay turns off, the diode conducts to suppress the high voltage spike from coil back EMF.
28️⃣
Q: The reverse recovery time of a diode is
Options:
A) Time to switch from ON to OFF
B) Time to remove charge carriers
C) Both A and B
D) None
Answer: C) Both A and B
Explanation:
It’s the time required for stored charges to dissipate when switching from forward to reverse bias.
29️⃣
Q: A diode used in high-frequency applications should have
Options:
A) Long recovery time
B) Short recovery time
C) High capacitance
D) Large junction area
Answer: B) Short recovery time
Explanation:
For high-speed switching, the diode should recover quickly from conducting to blocking state.
30️⃣
Q: The VI characteristic of a diode is
Options:
A) Linear
B) Non-linear
C) Parabolic
D) Constant
Answer: B) Non-linear
Explanation:
Diodes do not obey Ohm’s law; their I–V curve is exponential in the forward region.
31️⃣
Q: A Zener diode operates in
Options:
A) Forward bias region
B) Breakdown region
C) Reverse blocking region
D) Both forward and reverse
Answer: B) Breakdown region
Explanation:
Zener diodes are designed to operate stably in the reverse breakdown region for voltage regulation.
32️⃣
Q: The Zener breakdown is due to
Options:
A) Avalanche effect
B) Tunneling of electrons
C) Impact ionization
D) Thermal runaway
Answer: B) Tunneling of electrons
Explanation:
In Zener breakdown, strong electric fields cause electron tunneling through the junction.
33️⃣
Q: The avalanche breakdown occurs due to
Options:
A) Electron tunneling
B) High reverse voltage impact
C) Minority carrier diffusion
D) Recombination
Answer: B) High reverse voltage impact
Explanation:
High-energy carriers knock off other electrons, causing a chain reaction of ionization — avalanche breakdown.
34️⃣
Q: For voltage regulation, Zener diodes are connected
Options:
A) In forward bias
B) In reverse bias
C) In parallel to load
D) Both B and C
Answer: D) Both B and C
Explanation:
Zener diodes are reverse biased and placed parallel to the load to maintain constant voltage.
35️⃣
Q: The temperature coefficient of a Zener diode can be made zero by
Options:
A) Connecting two identical Zeners in parallel
B) Selecting Zener voltage ≈ 5.6V
C) Increasing current
D) Using silicon diode
Answer: B) Selecting Zener voltage ≈ 5.6V
Explanation:
At about 5.6V, the effects of Zener and avalanche breakdowns cancel, giving nearly zero temperature coefficient.
36️⃣
Q: The diode used as a voltage variable capacitor is
Options:
A) Zener diode
B) Varactor diode
C) Tunnel diode
D) LED
Answer: B) Varactor diode
Explanation:
A varactor diode operates under reverse bias, and its junction capacitance varies with applied voltage.
37️⃣
Q: Which diode emits light when forward biased?
Options:
A) Zener diode
B) LED
C) Tunnel diode
D) Schottky diode
Answer: B) LED
Explanation:
Light Emitting Diode (LED) releases photons due to electron-hole recombination in forward bias.
38️⃣
Q: The color of LED light depends on
Options:
A) Forward voltage
B) Type of semiconductor material
C) Current through diode
D) Packaging color
Answer: B) Type of semiconductor material
Explanation:
Different materials have different band gaps, which determine photon energy (and thus color).
39️⃣
Q: Schottky diodes are mainly used for
Options:
A) Low-speed switching
B) High-speed switching
C) Rectification only
D) Voltage regulation
Answer: B) High-speed switching
Explanation:
Schottky diodes have metal–semiconductor junctions with low forward drop and very short recovery time.
40️⃣
Q: The forward voltage drop of a Schottky diode is typically
Options:
A) 0.1–0.3 V
B) 0.5–0.7 V
C) 1.0–1.2 V
D) 2.0 V
Answer: A) 0.1–0.3 V
Explanation:
Due to metal–semiconductor contact, the voltage drop is very small, ideal for fast switching.
41️⃣
Q: The diode used for microwave frequency operation is
Options:
A) PIN diode
B) Varactor diode
C) Gunn diode
D) All of these
Answer: D) All of these
Explanation:
PIN, Varactor, and Gunn diodes are used in RF/microwave applications due to their high-frequency response.
42️⃣
Q: The diode used as a switch in RF attenuators is
Options:
A) Varactor
B) PIN diode
C) LED
D) Tunnel diode
Answer: B) PIN diode
Explanation:
The intrinsic layer in PIN diode gives controlled resistance, suitable for RF switching/attenuation.
43️⃣
Q: The reverse bias current in a diode is mainly due to
Options:
A) Majority carriers
B) Minority carriers
C) Both equally
D) Recombination
Answer: B) Minority carriers
Explanation:
Only minority carriers can cross the junction in reverse bias, producing small leakage current.
44️⃣
Q: Which of the following is a majority carrier device?
Options:
A) Tunnel diode
B) Schottky diode
C) PN junction diode
D) Zener diode
Answer: B) Schottky diode
Explanation:
Schottky diode conduction is by majority carriers (electrons), giving fast response.
45️⃣
Q: The diode equation is
Options:
A)
B)
C)
D)
Answer: A)
Explanation:
This exponential relationship defines current–voltage characteristics of an ideal diode.
46️⃣
Q: The constant in diode equation represents
Options:
A) Boltzmann constant
B) Stefan constant
C) Planck constant
D) None
Answer: A) Boltzmann constant
Explanation:
, used in thermionic and semiconductor equations.
47️⃣
Q: The ideal diode conducts
Options:
A) Partially in reverse
B) Fully in both directions
C) Fully in forward, not in reverse
D) None
Answer: C) Fully in forward, not in reverse
Explanation:
An ideal diode has zero resistance in forward direction and infinite resistance in reverse.
48️⃣
Q: The capacitance of a p–n junction under reverse bias is called
Options:
A) Transition capacitance
B) Diffusion capacitance
C) Junction capacitance
D) A and C both
Answer: D) A and C both
Explanation:
Transition or junction capacitance exists due to charge separation across the depletion region.
49️⃣
Q: Diffusion capacitance is significant under
Options:
A) Reverse bias
B) Forward bias
C) Both
D) None
Answer: B) Forward bias
Explanation:
Under forward bias, stored charge carriers create diffusion capacitance.
50️⃣
Q: The most commonly used material for semiconductor diodes is
Options:
A) Germanium
B) Silicon
C) Gallium arsenide
D) Selenium
Answer: B) Silicon
Explanation:
Silicon is widely used due to its thermal stability, low leakage, and abundant availability.
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