Assertion (A) : Op-amp has high input impedance.
Reason (R) : Op-amps have low input offset current.
MH SET - 2018, SET Exam - 2018,
Answer: B
The answer is both (A) and (R) are true but (R) is not the correct explanation of (A).
An op-amp does have a high input impedance, typically megohms for a bipolar input stage and far higher with FET inputs; it comes from the differential input stage working at very small bias currents. Op-amps also have a low input offset current, the difference between the two input bias currents, because the input transistors are matched.
Both are true, but offset current is a measure of mismatch between the inputs, not of how much current the input draws for a given voltage, so it does not explain the high impedance.
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