# Electronics and Communication Engineering - Exam Questions Papers

21.

A heavily doped semiconductor exhibits a __________ such a device is called sensistors.

 A. negative temperature coefficient of resistance B. positive temperature coefficient of resistance till a particular value of temperature and then it shown negative temperature coefficient of resistance C. positive temperature coefficient of resistance D. none of the above

Explanation:

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22.

Sampling frequency of
sin 100pt + cos 200pt + sin 100pt + cos 200pt is:

 A. 100 Hz B. 200 Hz C. 400 Hz D. none of these

Explanation:

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23.

For real and odd signals, the Fourier series coefficient ak is __________ .

 A. purely imaginary and even B. purely real and even C. purely imaginary and odd D. purely real and odd

Explanation:

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24.

The magnitude of frequency response of an underdamped second order system is 5 at 0 rad/sec and peaks to at 52rad/sec. The transfer function of the system is

 A. B. C. D.

Explanation:

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25.

Who developed the concept of time varying electric field producing a magnetic field?

 A. Gauss B. Faraday C. Hertz D. Maxwell