In a feedback amplifier, if the feedback voltage is in opposite phase…

The correct answer is Option (1) → Never work as an Oscillator

An amplifier becomes an oscillator only when a part of its output is fed back to the input in phase (positive feedback) and the loop gain is at least 1.

Here the feedback is in opposite phase (negative feedback) and the gain is less than 1.

Option (1) Never work as an Oscillator — Correct. Neither condition for oscillation is met, so the circuit cannot sustain oscillations under any condition.

Option (2) Work as an Oscillator — Incorrect. Oscillation needs in-phase feedback with a loop gain of at least 1; both are missing here.

Option (3) Work as an oscillator only at high frequency — Incorrect. Negative feedback with a gain below 1 damps the signal at every frequency, so it does not oscillate at high frequency either.

Option (4) Work as a rectifier — Incorrect. A rectifier converts ac into dc using diodes; feedback in an amplifier does not make it a rectifier.

Note: The original NTA paper printed Option (3) as “Not work as an Oscillator”. NTA accepted it as well, because it says the same as Option (1). For the benefit of students and to ensure a single answer, Option (3) has been changed to “Work as an oscillator only at high frequency”.

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic was removed from the latest NCERT book (2026-27), and it also appears to be out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Feedback Amplifier and Transistor Oscillator – “… In an oscillator, we get ac output without any external input signal. In other words, the output in an oscillator is self-sustained. To attain this, an amplifier is taken. A portion of the output power is returned back (feedback) to the input in phase with the starting power (this process is termed positive feedback) as shown in Fig. 14.33(a).”