Diodes and power supplies - 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
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
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
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
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
ANSWER: No voltage output
(6) ___________ material is used for infra-red LED’s
(A) Silicon
(B) Germanium
(C) Gallium arsenide
(D) Boron
ANSWER: Gallium arsenide
(7) Triac can be used like a
(A) Bidirectional SCR
(B) Unidirectional SCR
(C) PNP transistor
(D) NPN transistor
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
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
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%
ANSWER: 2.4%
(11) Gate trigger voltage for a SCR is
(A) 600 V
(B) 60 V
(C) 6 V
(D) 0.2 V
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
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
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
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
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
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
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.
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.
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
ANSWER: 234-0-234V
|
No comments:
Post a Comment