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

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

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(7) Triac can be used like a

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

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(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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(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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(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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(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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(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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(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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(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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(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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(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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(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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(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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(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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(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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