Exam-style question
Try this first
Which of the following best describes a key difference between an ideal op-amp and a real op-amp regarding input bias current?.
- A.Ideal op-amp has infinite input resistance, real has finite
- B.Ideal op-amp has zero input bias current, real has small but non‑zero
- C.Ideal op-amp has zero offset voltage, real has large offset voltage
- D.Ideal op-amp has infinite slew rate, real has limited slew rate
Model answer
What a good answer should say
- Ideal op-amp has zero input bias current, real has small but non‑zero
Explanation
Why this works
Define an ideal op‑amp as having zero input bias current, meaning no current flows into its inputs. Define a real op‑amp as having a small but measurable input bias current.
The key difference is that the ideal op‑amp draws no current, whereas the real op‑amp draws a tiny current. This difference matters when measuring currents or when high‑impedance signals are involved.
Therefore the correct statement is that the ideal op‑amp has zero input bias current while the real op‑amp has a small but non‑zero bias current.
Common mistake
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