Zener Diode:
1. What happens when a Zener diode is operated in reverse bias beyond its Zener voltage?
a) It gets damaged
b) It starts conducting
c) It behaves like an open circuit
d) It increases its resistance
Answer: b) It starts conducting
Explanation: A Zener diode is designed to conduct in reverse when the reverse voltage exceeds the Zener voltage, allowing it to regulate voltage.
2. Which breakdown mechanism is observed in Zener diodes at low reverse voltages (< 5V)?
a) Avalanche Breakdown
b) Electrical Breakdown
c) Zener Breakdown
d) Thermal Breakdown
Answer: c) Zener Breakdown
Explanation: Zener breakdown occurs in Zener diodes at low voltages due to quantum tunneling.
3. What does the term “PIV” stand for in rectifier circuits?
a) Peak Input Voltage
b) Peak Inverse Voltage
c) Primary Inverter Voltage
d) Positive Instant Voltage
Answer: b) Peak Inverse Voltage
Explanation: PIV is the maximum reverse voltage a diode can withstand without breaking down.
4. What is the symbol of a Zener diode different from a normal diode?
a) Curved line on the cathode
b) Two parallel lines
c) Bent line at cathode end
d) Circle around the diode
Answer: c) Bent line at cathode end
Explanation: The Zener diode symbol has a bent bar at the cathode to differentiate it from a normal diode.
5. Which of the following is NOT a specification of a Zener diode?
a) Zener voltage
b) Forward bias voltage
c) Maximum reverse current
d) Power dissipation
Answer: b) Forward bias voltage
Explanation: Forward voltage is not significant in Zener diode specs; it operates mainly in reverse.
Rectifiers:
6. What is the purpose of a rectifier?
a) To amplify current
b) To convert AC to DC
c) To reduce resistance
d) To increase frequency
Answer: b) To convert AC to DC
Explanation: A rectifier converts alternating current (AC) into direct current (DC).
7. Which rectifier gives the highest output voltage for the same input?
a) Half-wave
b) Full-wave bridge
c) Centre-tapped
d) Filtered rectifier
Answer: b) Full-wave bridge
Explanation: Full-wave bridge uses the full AC cycle without the need for a center tap.
8. How many diodes are used in a full-wave bridge rectifier?
a) 2
b) 3
c) 4
d) 6
Answer: c) 4
Explanation: A bridge rectifier uses four diodes to convert full AC cycle into DC.
9. Which rectifier needs a center-tapped transformer?
a) Half-wave
b) Bridge
c) Centre-tapped full-wave
d) None of these
Answer: c) Centre-tapped full-wave
Explanation: This rectifier needs a center-tap to provide two halves of the AC waveform.
10. What is ripple factor?
a) Ratio of output voltage to input voltage
b) Ratio of AC to DC in output
c) Ratio of frequency to voltage
d) Ratio of RMS to average value
Answer: b) Ratio of AC to DC in output
Explanation: Ripple factor measures the amount of AC component remaining in DC output.
11. Which of the following rectifiers has the lowest efficiency?
a) Full-wave
b) Bridge
c) Half-wave
d) Centre-tapped
Answer: c) Half-wave
Explanation: Half-wave uses only one half of the AC cycle, resulting in lower efficiency.
12. The average output voltage of a full-wave rectifier is approximately:
a) 0.318 Vmax
b) 0.636 Vmax
c) 0.707 Vmax
d) 1.0 Vmax
Answer: b) 0.636 Vmax
Explanation: Full-wave average output voltage = 2Vm/π ≈ 0.636Vm.
13. What happens to the ripple frequency in a full-wave rectifier?
a) It is the same as AC input
b) It is double the AC input
c) It becomes zero
d) It is halved
Answer: b) It is double the AC input
Explanation: In full-wave rectification, ripple frequency = 2 × supply frequency.
Filters:
14. What is the role of a filter in rectification circuits?
a) Increase AC component
b) Smooth out DC output
c) Regulate voltage
d) Reduce power loss
Answer: b) Smooth out DC output
Explanation: Filters reduce the ripple in DC output after rectification.
15. Which filter uses both an inductor and capacitor?
a) LC filter
b) Shunt capacitor filter
c) Series inductor filter
d) π filter
Answer: a) LC filter
Explanation: LC filter uses an inductor and capacitor to remove ripple.
16. A π filter consists of:
a) Two inductors and a capacitor
b) Two capacitors and an inductor
c) Only capacitors
d) Only inductors
Answer: b) Two capacitors and an inductor
Explanation: π filter = capacitor – inductor – capacitor, resembling π shape.
17. What is the main limitation of a shunt capacitor filter?
a) High ripple
b) Bulky
c) Cannot work at high current
d) Expensive
Answer: c) Cannot work at high current
Explanation: Shunt capacitors may overheat or fail at high load currents.
18. Which filter is best for constant load current?
a) Series inductor filter
b) LC filter
c) Shunt capacitor filter
d) π filter
Answer: a) Series inductor filter
Explanation: Inductors oppose current change, hence good for constant load.
19. What is the advantage of a π filter over LC filter?
a) Lower cost
b) Better ripple reduction
c) Smaller size
d) Works at high frequencies
Answer: b) Better ripple reduction
Explanation: π filters offer better ripple reduction due to double capacitive filtering.
20. Which component stores energy in the magnetic field?
a) Capacitor
b) Inductor
c) Diode
d) Resistor
Answer: b) Inductor
Explanation: Inductors store energy in a magnetic field when current flows through.
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