Voltage follower property — a unity-gain buffer (voltage follower) has a fixed closed-loop voltage gain approximately equal to 1, not 10. Is the statement “gain ≈ 10” appropriate for a voltage follower?
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AIncorrect — a voltage follower has gain ≈ 1
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BCorrect — a voltage follower has gain ≈ 10
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CCorrect only with dual ± supplies
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DCorrect only at high frequency
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ECannot be determined without the op-amp model
Answer
Correct Answer: Incorrect — a voltage follower has gain ≈ 1
Explanation
Introduction / Context:A voltage follower (also called a unity-gain buffer) connects the op-amp output directly to the inverting input and applies the signal to the non-inverting input. The closed-loop gain is approximately +1, providing high input impedance, low output impedance, and isolation without amplifying the voltage magnitude. The prompt claims a fixed gain near 10, which describes a different non-inverting amplifier configuration with an external resistor divider, not a follower.
Given Data / Assumptions:
- Standard op-amp operated within linear region and bandwidth limits.
- Unity-feedback topology for a voltage follower.
- Neglect small gain error due to finite open-loop gain and frequency response.
Concept / Approach:For a non-inverting amplifier with feedback network, the closed-loop gain is Av = 1 + (Rf/Rg). A follower is the special case Rf → ∞ and Rg → ∞ replaced by a direct short from output to inverting input, yielding Av ≈ 1. Any gain near 10 would require explicit resistor values (e.g., Rf/Rg ≈ 9), which is not a unity follower.
Step-by-Step Solution:
1) Recognize unity-feedback topology of a follower.2) Write closed-loop gain for non-inverting form: Av = 1 + (Rf/Rg).3) For a follower (Rf = 0 from output to − input; Rg open), Av ≈ 1.4) Conclude that “gain ≈ 10” is incorrect for a voltage follower.Verification / Alternative check:Measure Vout/Vin of an actual follower over frequency within the device’s bandwidth; it will track ~1 with minimal phase/amp error until roll-off.
Why Other Options Are Wrong:
Claiming gain ≈ 10 conflates follower with a designed non-inverting amplifier of gain 10.Dual supplies or high frequency do not convert a follower into gain 10 without adding a divider.“Cannot be determined”: topology alone establishes the expected gain.Common Pitfalls:Using the term “buffer” for any non-inverting stage regardless of gain; ignoring finite bandwidth and stability considerations which slightly alter unity gain at extremes.
Final Answer:Incorrect — a voltage follower has gain ≈ 1