Which statement is true?

Which statement is true?

• A. An op-amp can detect voltage differences between its input terminals.
• B. A zener diode can be used in the feedback path of a voltage comparator.
• C. In a comparator circuit, a reference voltage shifts the trigger point of the circuit.
• D. Voltage comparators perform as low-pass filters.

Answer: (A)

The essential idea is that an op-amp responds to the voltage difference between its two input terminals and produces an output that is proportional to that difference (with a very large gain). This is what lets the device amplify tiny input differences into a large output, and it also underpins how a comparator uses the sign of that difference to decide which output state to take. In normal operation with feedback, the difference is driven toward zero, creating a stable, linear region; without feedback, even a tiny difference drives the output to one of the rails, effectively “detecting” which input is higher. This is why the statement is true: an op-amp’s fundamental role is to sense the voltage difference at its inputs and respond accordingly. The other ideas are less generally true or describe different or nonstandard configurations: using a zener in the feedback path of a comparator isn’t part of its basic function; a reference voltage can set a threshold in some designs but isn’t the defining behavior of an op-amp; and comparators are not low-pass filters, as they are meant to respond to the sign of the input difference rather than to filter frequencies.

The essential idea is that an op-amp responds to the voltage difference between its two input terminals and produces an output that is proportional to that difference (with a very large gain). This is what lets the device amplify tiny input differences into a large output, and it also underpins how a comparator uses the sign of that difference to decide which output state to take. In normal operation with feedback, the difference is driven toward zero, creating a stable, linear region; without feedback, even a tiny difference drives the output to one of the rails, effectively “detecting” which input is higher.

This is why the statement is true: an op-amp’s fundamental role is to sense the voltage difference at its inputs and respond accordingly. The other ideas are less generally true or describe different or nonstandard configurations: using a zener in the feedback path of a comparator isn’t part of its basic function; a reference voltage can set a threshold in some designs but isn’t the defining behavior of an op-amp; and comparators are not low-pass filters, as they are meant to respond to the sign of the input difference rather than to filter frequencies.