Diodes and power supplies - Electronics Engineering test questions

Diodes and power supplies - Electronics Engineering test questions


(1) In case of LED’s, the power consumption may be of the order of

(A) 5 to 10 amperes
(B) 5 to 10 nano amperes
(C) 5 to 10 micro amperes
(D) 5 to 10 milliamperes

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ANSWER: 5 to 10 milliamperes




(2) Characteristics of an ideal current source is close to that of

(A) Transistor in CB mode
(B) Gas diode
(C) Crystal diode
(D) None of the above

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ANSWER: Transistor in CB mode




(3) Which of the following device cannot be used as a UJT?

(A) Switching device
(B) Timing device
(C) Transistor amplifier
(D) All of the above

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ANSWER: Transistor amplifier




(4) Normally vacuum tube heaters take a voltage of

(A) 220 V
(B) 6.3 V
(C) 1 V
(D) 2.3 V

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ANSWER: 6.3 V




(5) If the input capacitor of a power supply is shorted, it will result in

(A) Reduced voltage output
(B) No voltage output
(C) Excessive hum
(D) None of the above

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ANSWER: No voltage output




(6) ___________ material is used for infra-red LED’s

(A) Silicon
(B) Germanium
(C) Gallium arsenide
(D) Boron

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ANSWER: Gallium arsenide




(7) Triac can be used like a

(A) Bidirectional SCR
(B) Unidirectional SCR
(C) PNP transistor
(D) NPN transistor

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ANSWER: Bidirectional SCR




(8) In a photoconductive diode

(A) As light increases, resistance increases
(B) As light increases, resistance decreases
(C) Resistance remains constant even when light varies
(D) None of the above

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ANSWER: As light increases, resistance decreases




(9) An emitter and two connections to the base without a collector terminal, is present in

(A) SCR
(B) Triac
(C) Diac
(D) UJT

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ANSWER: UJT




(10) At full load the dc output voltage is 40 V and it is 41 V without any load current. The load regulation is

(A) 0.96%
(B) 0.24%
(C) 2.4%
(D) 0.48%

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ANSWER: 2.4%




(11) Gate trigger voltage for a SCR is

(A) 600 V
(B) 60 V
(C) 6 V
(D) 0.2 V

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ANSWER: 600 V




(12) If anode voltage = 500 V and gate voltage = -5 V. It can be concluded that SCR is

(A) OFF
(B) ON at part load
(C) ON at no load
(D) ON at full load

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ANSWER: OFF




(13) In a power supply, excessive hum could be due to

(A) Defective rectifier
(B) Open filter choke
(C) Capacitor
(D) None of the above

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ANSWER: Capacitor




(14) The effective value of half-wave rectified sine wave is 20, the average value of the wave will be

(A) 69.9
(B) 12.7
(C) 23.3
(D) 27.8

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ANSWER: 12.7




(15) In case of vacuum tube diode, the internal voltage drop is of the order

(A) 5 to 10 V
(B) 2 10 5 V
(C) 15 to 20 V
(D) 1 to 2 V

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ANSWER: 15 to 20 V




(16) A voltage function is given by
V (t) = 100 +25 sin 3 ωt + 10 sin 5 ωt volts. The RMS value will be

(A) 101.8 V
(B) 90.8 V
(C) 59.9 V
(D) 68.9 V

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ANSWER: 101.8 V




(17) In conduction state, the voltage drop across a SCR is about
(A) 30 V
(B) 100 V
(C) 1μ V
(D) 1 V

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ANSWER: 1 V




(18) The UJT is a four layer device

(A) True
(B) False
(C) Layers can be changed according to requirement
(D) None of the above.

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ANSWER: False




(19) Which one of the following statement is false?

(A) LED’s are fast in action
(B) For 50 Hz input the ripple frequency in a bridge rectifier will be 100Hz
(C) With 60 Hz input a half wave rectifier will have ripple frequency of 120 Hz
(D) SCR is a four layer device used as a silicon rectifier.

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ANSWER: With 60 Hz input a half wave rectifier will have ripple frequency of 120 Hz




(20) A full wave rectifier using a capacitor input filter is to supply 100mA at 300V.The secondary voltage of the transformer must be

(A) 200-0-200V
(B) 234-0-234V
(C) 300-0-300V
(D) 420-0-420V

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ANSWER: 234-0-234V



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    Discussion

  • Diodes and power supplies - Electronics Engineering test questions -Slesha Shirkey (11/12/13)
  • (21) In case of __________ PN junction is heavily doped

    (A) Tunnel diode
    (B) Gun diodes
    (C) PIN diodes
    (D) All of the above

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    ANSWER: Tunnel diode




    (22) Consider a function, y = 50 + 30 sin ωt. The effective value is

    (A) 54.3
    (B) 44.7
    (C) 27.3
    (D) 38.5

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    ANSWER: 54.3




    (23) As compared to mercury arc rectifiers, metal rectifiers

    (A) Can operate on high voltages
    (B) Can operate at high loads
    (C) Give poor regulation
    (D) Operate on low temperatures

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    ANSWER: Operate on low temperatures




    (24) LED’s do not require

    (A) Warm up time
    (B) Heating
    (C) Both A and B
    (D) None of the above

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    ANSWER: Both A and B




    (25) In SCR, the conduction is controlled by

    (A) Gate
    (B) Cathode
    (C) Anode
    (D) None of the above

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    ANSWER: Gate




    (26) ____________ uses two junctions of opposite polarities

    (A) Zener diode
    (B) Varistor
    (C) Tunnel diode
    (D) LED

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    ANSWER: Varistor




    (28) Which of the following statement is false

    (A) A zener diode has characteristics similar to that of an ideal current source
    (B) The SCR anode conducts with either positive or negative voltage
    (C) The SCR has gate electrode but triac has none
    (D) All of the above

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    ANSWER: All of the above




    (29) Esaki diode is same as

    (A) Tunnel diode
    (B) Gun diode
    (C) PIN diode
    (D) None of the above

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    ANSWER: Tunnel diode




    (30) An average power of 25 ohm resistor is 100 W. The maximum value of current function if it is sinusoidal will be

    (A) 2 A
    (B) 1.68 A
    (C) 2.83 A
    (D) 1.41 A

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    ANSWER: 2.83 A




    (31) When reverse bias is applied to a P-N junction diode,

    (A) Potential barriers is decreased
    (B) Potential barriers is increased
    (C) Minority carrier current is greatly increased
    (D) Majority carrier current is greatly increased

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    ANSWER: Potential barriers is increased




    (32) Zener diode is used as a

    (A) Series regulator
    (B) Shunt regulator
    (C) Either A or B
    (D) None of the above

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    ANSWER: Shunt regulator




    (33) The “Impact avalanche and transit time” diode and ________ diode both exhibit negative resistance

    (A) Gun
    (B) Crystal
    (C) Esaki
    (D) Tunnel

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    ANSWER: Gun




    (34) In a power supply with normal ac input if there is no V+ output, the trouble could be with

    (A) Open filter choke
    (B) Excessive hum
    (C) Rectifier
    (D) None of the above

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    ANSWER: Rectifier




    (35) Let ym = peak value of a full wave rectified sine wave, the average value will be

    (A) 0.717 ym
    (B) 0.5 ym
    (C) 0.83 ym
    (D) 0.637 ym

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    ANSWER: 0.637 ym




    (36) Major portion of the V-I characteristics of a gas diode represents constant voltage characteristics

    (A) True
    (B) False
    (C) Depends on current passed through a gas diode
    (D) None of the above

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    ANSWER: True




    (37) In the periodic table germanium, silicon and _______ belongs to same group

    (A) Sulphur
    (B) Copper
    (C) Carbon
    (D) Gold

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    ANSWER: Carbon




    (38) Wiedemann-Franz law correlates

    (A) Electron arrangement in shells
    (B) Electrical and thermal conductivities
    (C) Temperature and photo electric emission
    (D) None of the above

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    ANSWER: Electrical and thermal conductivities




    (39) When a semiconductor diode is tested with ohmmeter it gives low value of R in both directions. Therefore it is concluded that

    (A) The diode is open
    (B) The diode is shorted
    (C) Nothing can be concluded
    (D) The diode is satisfactory

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    ANSWER: The diode is shorted




    (40) In case of a junction diode, the depletion or space charge region contains charges that are

    (A) Fixed donor and acceptor ions
    (B) Mobile donor and acceptor ions
    (C) Mostly majority carriers
    (D) Mostly minority carriers

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    ANSWER: Fixed donor and acceptor ions