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ECE Objective Questions { Diode Circuits }

71. A zener diode when biased correctly
A. never overheats
B. acts as a fixed resistance
C. has a constant voltage across it
D. has a constant current passing through it

72. Regarding a tunnel diode which of the following statements is incorrect?
A. Width of its depletion layer is quite large
B. It has negative resistance over a specific range of its forward voltage
C. Its impurity concentration is about 1000 times greater than that of an ordinary junction diode
D. Charge carriers are able to tunnel through its depletion layer very easily due to its extremely small thickness

73. A phototube is an electronic tube
A. that is used in TV sets for producing picture on the screen
B. whose resistance decreases as its cathode is exposed to more light
C. whichis used for producing a brilliant flash of light for taking photographs in the dark
D. that emits photoelectrons when its cathode is illuminated

74. The maximum reverse voltage that can be applied to an ordinary semiconductor diode without irreverslible damage is called
A. cut-off voltage
B. avalanche breakdown voltage
C. peak inverse voltage
D. zener voltage

75. A tunnel diode
A. has a small tunnel in its junction
B. is a point contact diode with a high reverse resistance
C. is a gallium arsenide device
D. is a highly doped P-N junction device

76. The function of a zener diode, when used in a power supply, is to maintain a constant
A. supply current
B. output current irrespective of the load resistance
C. output voltage
D. input voltage

77. When bias applied to a van-cap diode is increased its capacitance
A.When heated, their light output tends to shift to shorter wavelength
B.They have rapid turn-on and turn-off times
C.They response times are about 5 nanoseconds
D.They emit lights of different wavelengths varying infra-red to green

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