🔍 Key Concepts

• Open-loop vs closed-loop operation in op-amp circuits • Role of feedback (negative or positive) in amplifier, filter, and comparator designs • How linear amplification differs from level comparison in op-amp applications

💭 Think About

• For each option, ask: does this circuit normally use feedback from output to input to control the gain? • Consider which circuit is intended to compare two voltages and switch output high/low rather than provide a precise, stable gain. • Think about which circuits rely on a defined, finite gain versus the op-amp’s very large internal gain.

✅ Before You Answer

• Identify which options are typical closed-loop amplifiers that set a specific gain with resistors and feedback. • Check which option’s main purpose is decision-making (greater/less than) rather than proportional amplification. • Verify which circuit type can intentionally use the op-amp’s very high open-loop gain without added feedback.