Why do we want infinitely high input impedance in an ideal opamp?

• A. The higher the impedance, the lower the current drawn from the source
• B. The higher the impedance, the higher the current drawn from the source
• C. Impedance has no effect on current drawn
• D. Infinite impedance causes instability

Answer: (A)

The essential idea is that input impedance determines how much current the signal source must supply. With an ideal op-amp, the input impedance is infinite, so the input current is essentially zero for any finite input voltage. This means the signal source is not loading the circuit—the source voltage remains unchanged by the connection, allowing accurate amplification. That’s why the best answer is that higher impedance means lower current drawn from the source.

In other words, infinite input impedance minimizes loading on the source. The other statements don’t fit: higher impedance does not force more current; impedance clearly affects how much current is drawn; infinite impedance by itself does not cause instability (instability relates to the feedback network and overall circuit dynamics).