Exam-style question
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Which statement best explains why the output of a non‑inverting amplifier is not phase inverted?.
- A.The input is applied to the inverting input.
- B.Negative feedback forces the output to match the input polarity.
- C.The op‑amp has a phase shift of 180°.
- D.The output is taken from the inverting input.
Model answer
What a good answer should say
- Negative feedback forces the output to match the input polarity.
Explanation
Why this works
Initial state: A positive input voltage V_in is applied to the non‑inverting (+) input; the output voltage V_out is unknown. Step‑by‑step execution: 1.
The op‑amp amplifies the difference between its inputs. 2.
Negative feedback connects the output to the inverting (−) input via a resistor network, so the op‑amp adjusts V_out until the voltage at the inverting input equals V_in. 3.
Because V_in is positive, the op‑amp drives V_out positive to satisfy the equality. Final state: V_out is positive and has the same sign as V_in.
Conclusion: The negative feedback loop forces the output to follow the input polarity, preventing phase inversion.
Common mistake
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