Mcqs of diode | diode Review Topics | Numericals of Diod

Mcqs of diode which is most important. Usually, these type of Mcqs of diode comes in screening tests not all of them but few from this post. these Mcqs of diode are prepared for the job seekers.

  1. A crystal diode has ……..
    (i) one pn junction
    (ii) two pn junctions
    (iii) three pn junctions
    (iv) none of the above
  2. A crystal diode has forward resistance of the order of ……..
    (i) kΩ (ii) Ω
    (iii) MΩ (iv) none of the above
  3. If the arrow of crystal diode symbol is positive w.r.t. bar, then diode is …….. biased (i) forward (ii) revers (iii) either forward or reverse (iv) none of the above
  1. The reverse current in a diode is of the order of ……..
    (i) kA (ii) mA
    (iii) µA (iv) A
  2. The forward voltage drop across a silicon diode is about …….. (i) 2.5 V (ii) 3 V (iii) 10 V (iv) 0.7 V
  1. A crystal diode is used as ……..
    (i) an amplifier (ii) a rectifier
    (iii) an oscillator (iv) a voltage regulator
  2. The d.c. resistance of a crystal diode is …….. its a.c. resistance.
    (i) the same as (ii) more than
    (iii) less than (iv) none of the above
  3. An ideal crystal diode is one which behaves as a perfect …….. when forward biased.
    (i) conductor
    (ii) insulator
    (iii) resistance material
    (iv) none of the above
  4. The ratio of reverse resistance and forward resistance of a germanium crystal diode is about ……..
    (i) 1 : 1 (ii) 100 : 1
    (iii) 1000 : 1 (iv) 40000 : 1
  5. The leakage current in a crystal diode is due to ……..
    (i) minority carriers
    (ii) majority carriers
    (iii) junction capacitance
    (iv) none of the above
  6. If the temperature of a crystal diode increases, then leakage current ……..
    (i) remains the same
    (ii) decreases
    (iii) increases
    (iv) becomes zero
  7. The PIV rating of a crystal diode is …….. that of equivalent vacuum diode.
    (i) the same as (ii) lower than
    (iii) more than (iv) none of the above
  8. If the doping level of a crystal diode is increased, the breakdown voltage ………
    (i) remains the same
    (ii) is increased
    (iii) is decreased
    (iv) none of the above
  9. The knee voltage of a crystal diode is approximately equal to ……..

(i) applied voltage
(ii) breakdown voltage
(iii) forward voltage
(iv) barrier potential

  1. When the graph between current through and voltage across a device is a straight line, the device is referred to as ……..
    (i) linear (ii) active
    (iii) nonlinear (iv) passive
  2. When the crystal diode current is large, the bias is ……..
    (i) forward (ii) inverse
    (iii) poor (iv) reverse
  3. A crystal diode is a …….. device.
    (i) non-linear (ii) bilateral
    (iii) linear (iv) none of the above
  4. A crystal diode utilises …….. characteristic for rectification.
    (i) reverse (ii) forward
    (iii) forward or reverse
    (iv) none of the above
  5. When a crystal diode is used as a rectifier, the most important consideration is ……..
    (i) forward characteristic
    (ii) doping level
    (iii) reverse characteristic
    (iv) PIV rating
  6. If the doping level in a crystal diode is increased, the width of depletion layer ……..
    (i) remains the same
    (ii) is decreased
    (iii) is increased
    (iv) none of the above
  7. A zener diode has ……..
    (i) one pn junction
    (ii) two pn junctions
    (iii) three pn junctions
    (iv) none of the above
  8. A zener diode is used as ……..
    (i) an amplifier (ii) a voltage regulator
    (iii) a rectifier (iv) a multivibrator
  9. The doping level in a zener diode is …….. that of a crystal diode.

(i) the same as (ii) less than
(iii) more than (iv) none of the above

  1. A zener diode is always ………. connected.
    (i) reverse
    (ii) forward
    (iii) either reverse or forward
    (iv) none of the above
  2. A zener diode utilises …….. characteristic for its operation.
    (i) forward
    (ii) reverse
    (iii) both forward and reverse
    (iv) none of the above
  3. In the breakdown region, a zener diode behaves like a ……… source.
    (i) constant voltage
    (ii) constant current
    (iii) constant resistance
    (iv) none of the above
  4. A zener diode is destroyed if it ……..
    (i) is forward biased
    (ii) is reverse biased
    (iii) carries more than rated current
    (iv) none of the above
  5. A series resistance is connected in the Zener circuit to ……..
    (i) properly reverse bias the zener
    (ii) protect the zener
    (iii) properly forward bias the zener
    (iv) none of the above
  6. A zener diode is …….. device.
    (i) a non-linear (ii) a linear
    (iii) an amplifying (iv) none of the above
  7. A zener diode has …….. breakdown voltage.
    (i) undefined (ii) sharp
    (iii) zero (iv) none of the above
  8. …….. rectifier has the lowest forward resistance.
    (i) solid state (ii) vacuum tube
    (iii) gas tube (iv) none of the above
  9. Mains a.c. power is converted into d.c. power for ……..
    (i) lighting purposes (ii) heaters (iii) using in electronic equipment (iv) none of the above
  1. The disadvantage of a half-wave rectifier is that the ……..
    (i) components are expensive
    (ii) diodes must have a higher power rating
    (iii) output is difficult to filter
    (iv) none of the above
  2. If the a.c. input to a half-wave rectifier has an r.m.s. value of 400/ 2 volts, then diode
    PIV rating is ……..

    (i) 400/ 2 V (ii) 400 V
    (iii) 400 × 2 V (iv) none of the above
  3. The ripple factor of a half-wave rectifier is……..
    (i)2 (ii) 1.21
    (iii) 2.5 (iv) 0.48
  4. There is a need of transformer for ……..
    (i) half-wave rectifier
    (ii) centre-tap full-wave rectifier
    (iii) bridge full-wave rectifier
    (iv) none of the above
  5. The PIV rating of each diode in a bridge rectifier is …….. that of the equivalent centre tap rectifier.
    (i) one-half (ii) the same as
    (iii) twice (iv) four times
  6. For the same secondary voltage, the output voltage from a centre-tap rectifier is …….. than that of bridge rectifier.
    (i) twice (ii) thrice
    (iii) four times (iv) one-half
  7. If the PIV rating of a diode is exceeded, ……..
    (i) the diode conducts poorly
    (ii) the diode is destroyed
    (iii) the diode behaves as zener diode
    (iv) none of the above
  8. A 10 V power supply would use …….. as filter capacitor.
    (i) paper capacitor (ii) mica capacitor
    (iii) electrolytic capacitor
    (iv) air capacitor
  1. A 1000 V power supply would use …….. as a filter capacitor.
    (i) paper capacitor
    (ii) air capacitor
    (iii) mica capacitor
    (iv) electrolytic capacitor
  2. The …… filter circuit results in the best voltage regulation.
    (i) choke input
    (ii) capacitor input
    (iii) resistance input
    (iv) none of the above
  3. A half-wave rectifier has an input voltage of 240 V r.m.s. If the step-down transformer has a turns ratio of 8 : 1, what is the peak load voltage ? Ignore diode drop. (i) 27.5 V (ii) 86.5 V (iii) 30 V (iv) 42.5 V
  1. The maximum efficiency of a half-wave rectifier is ………..
    (i) 40.6% (ii) 81.2%
    (iii) 50% (iv) 25%
  2. The most widely used rectifier is ………..
    (i) half-wave rectifier
    (ii) centre-tap full-wave rectifier
    (iii) bridge full-wave rectifier
    (iv) none of the above

Semiconductor diode Review Topics

  1. What is a crystal diode ? Explain its rectifying action.
  2. Draw the graphic symbol of crystal diode and explain its significance. How the polarities of crystal diode are identified ?
  3. What do you understand by the d.c. and a.c. resistance of a crystal diode ? How will you determine them from the V-I characteristic of a crystal diode ?
  4. Draw the equivalent circuit of a crystal diode.
  5. Discuss the importance of peak inverse voltage in rectifier service.
  6. Describe a half-wave rectifier using a crystal diode.
  7. Derive an expression for the efficiency of a half-wave rectifier.
  8. With a neat sketch, explain the working of (i) Centre-tap full-wave rectifier (ii) Full-wave bridge rectifier.
  9. Derive an expression for the efficiency for a full-wave rectifier.
  10. Write a short note about the nature of rectifier output.
  11. What is a ripple factor ? What is its value for a half-wave and full-wave rectifier ?
  12. Describe the action of the following filter circuits : (i) capacitor filter (ii) choke input filter (iii) capacitor input filter.
  13. What is a zener diode ? Draw the equivalent circuit of an ideal zener in the breakdown region.
  14. Explain how zener diode maintains constant voltage across the load.

Problems of semiconductor diode

  1. What is the current in the circuit in Fig. 6.72 ? Assume the diode to be ideal. [10 mA]
  1. Using equivalent circuit, determine the current in the circuit shown in Fig. 6.73. Assume the forward resistance of the diode to be 2 Ω. [358 mA]
  2. Find the voltage VA and current I in the circuit shown in Fig. 6.74. Use simplified model. [14 V; 2 mA]
  3. Determine the magnitude of VA in the circuit shown in Fig. 6.75. [9.5 V]
  4. A half-wave rectifier uses a transformer of turn ratio 4 : 1. If the primary voltage is 240 V (r.m.s.), find (i) d.c. output voltage (ii) peak inverse voltage. Assume the diode to be ideal. [(i) 27 V (ii) 85V]
  1. A half-wave rectifier uses a transformer of turn ratio 2 : 1. The load resistance is 500 Ω. If the primary voltage (r.m.s.) is 240 V, find (i) d.c. output voltage (ii) peak inverse voltage. [(i) 54 V (ii) 170 V]
  1. In Fig. 6.76, the maximum voltage across half of secondary winding is 50 V. Find (i) the average load voltage (ii) peak inverse voltage (iii) output frequency. Assume the diodes to be ideal. [(i) 31.8 V (ii) 100 V (iii) 100 Hz]

  1. In Fig. 6.77, the maximum secondary voltage is 136 V. Find (i) the d.c. load voltage (ii) peak inverse voltage (iii) output frequency. [(i) 86.6 V (ii) 136 V (iii) 100 Hz]
  2. A semiconductor diode having ideal forward and reverse characteristics is used in a half-wave rectifier circuit supplying a resistive load of 1000 Ω. If the r.m.s. value of the sinusoidal supply voltage is 250 V, determine (i) the r.m.s. diode current and (ii) power dissipated in the load.
    [(i) 177 mA (ii) 31.3W]
  3. The four semiconductor diodes used in a bridge rectifier circuit have forward resistance which can be considered constant at 0.1Ω and infinite reverse resistance. They supply a mean current of 10 A to a resistive load from a sinusoidally varying alternating supply of 20V r.m.s. Determine the resistance of the load and the efficiency of the circuit. [1.6Ω ; 72%]
  4. Find the average value of each voltage in Fig. 6.78.
    [(i) 1.59 V (ii) 63.7 V (iii) 16.4 V (iv) 10.5 V]
  1. Calculate the peak voltage across each half of a centre-tapped transformer used in a full-wave rectifier that has an average output voltage of 110V. [173V]
  2. What PIV rating is required for the diodes in a bridge rectifier that produces an average output voltage of 50V? [78.5 V]
  3. In the circuit shown in Fig. 6.79, is zener diode in the on or off state ? [Off]
  1. In the circuit shown in Fig. 6.80, determine the range of RL that will result in a constant voltage of 10 V across RL. [250 Ω to 1.25 kΩ]

Discussion Questions of Semiconductor diode

  1. Why are diodes not operated in the breakdown region in rectifier service ?
  2. Why do we use transformers in rectifier service ?
  3. Why is PIV important in rectifier service ?
  4. Why is zener diode used as a voltage regulator ?
  5. Why is capacitor input filter preferred to choke input filter ?

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