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ECE Objective Questions { BJT Amplifiers and Transistor }

43.  In a voltage shunt feedback, the input impedance is
A. decreased
B. increased
C. remains unchanged
D. all the above

44.  Statement-1 Theoretical efficiency of a class-A power amplifier is 78% Statement-2 A single-ended power amplifier uses one transistor only.
A. statement 1 is correct but 2 is wrong
B. statement 2 is correct but 1 is wrong
C. both statements 1 and 2 are correct
D. neither statement 1 nor 2 is correct

45. Johnson noise in an amplifier is the noise produced due to
A. switching off or on of an electrical apparatus
B. lighting
C. the fact that electrons in a resistor carry slightly different amounts of energy
D. the fact that current is carried by discrete particles

46. The signal/noise (SIN) ratio of an amplifier developing an output voltage of 10V and a noise voltage of 1 mV is ____ dB.

47. The power gain of an amplifier is 80 dB. The half-power frequencies fi and f2 are the frequencies where gain has fallen to ___ dB.
D. 80 /

48. The condition fiA = 1 in an amplifier
A. can never occur
B. leads to oscillations
C. means that there is no feedback
D. means that feedback is positive

49.  For sustaining oscillations in a feedback amplifier, the loop gain should be
A. zero
B. less than one
C. greater than one
D. Negative

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