78. Negative resistance is obtained with a Gunn diode because of
A. electron transfer to a less mobile energy level
B. avalanche breakdown with the high voltage gradient
C. tunnelling across the junction
D. electron domains forming at the junction

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79. The negative resistance in a tunnel diode is
A. maximum at the peak point of the characteristics
B. available between peak and valley points
C. maximum at valley point
D. none of these

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80. When current through a zener diode increases by a facto of 2, the voltage across its terminals
A. is halved
B. gets doubled too
C. remains unaltered
D. none of these

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81. An avalanche diode
A. is the same as the zener diode
B. is operated in the forward?biased mode only
C. is usually operated in the reverse?biased mode only
D. none of these

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82. The dynamic impedance of a zener diode
A. increases with increase in current through it
B. decreases with increase in current through it
C. is independent of current passing through it
D. none of these

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83. There are two semiconductor diode A and B. One of them is zener whereas other is avalanche. Their ratings are 6.2 V and 24 V respectively, then
A. A is zener, B is avalanche
B. A is avalanche, B is zener
C. both of them are zeners
D. none of these

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84. Three identical zener diodes when connected in series were found to exhibit a breakdown at 18 V. Each of them has a breakdown potential of
A. 18 V
B. 6 V
C. 54 V
D. none of these

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