# Electronics and Communication Engineering - Electronic Devices and Circuits

1.

The ratio of impurity atoms to intrinsic semiconductor atoms in an extrinsic semiconductor is about.

 A. 1 : 10 B. 1 : 1000 C. 1 : 100000 D. 1 : 108

Explanation:

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2.

To ensure that a zener diode does not get destroyed

 A. the applied voltage should not exceed breakdown voltage B. the current should not exceed rated current C. the current should be less than magnitude of barrier potential D. both (a) and (b)

Explanation:

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3.

SCR turns of from conducting state to blocking state on

 A. reducing gate current B. reversing gate voltage C. reducing anode current below holding current value D. applying ac to the gate

Explanation:

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4.

The kinetic energy of free electrons in a metal is (where k is the de-Broglie wave number of the electron)

 A. inversely proportional to k B. inversely proportional to square of k C. proportional to k D. proportional to the square of k

Explanation:

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5.

The turn on time of an SCR is 5 micro second. Its trigger pulse should have

 A. short rise time with pulse width = 2.5 μs B. long rise time with pulse width = 3 μs C. short rise time with pulse width = 4 μs D. long rise time with pulse width = 4 μs