Deep Dive: E7G03
The correct answer is D: Very high. The typical input impedance of an operational amplifier (op-amp) is very high, typically in the megohm range (millions of ohms). This very high input impedance is a fundamental characteristic of op-amps that makes them ideal for voltage sensing applications. Op-amps are designed with very high input impedance so they draw minimal current from the signal source. This means the op-amp doesn't load down the source circuit, allowing accurate voltage measurements and signal processing. The very high input impedance (often 1 megohm or more) contrasts with the very low output impedance (typically a few ohms) of op-amps. This high input/low output impedance combination makes op-amps excellent buffer amplifiers and voltage followers.
Why Other Answers Are Wrong
Option A: Incorrect. 100 ohms is very low input impedance. Op-amps have very high input impedance, not low. Option B: Incorrect. 10,000 ohms (10 kΩ) is still too low. Op-amp input impedance is typically in the megohm range. Option C: Incorrect. Very low is the output impedance characteristic, not input impedance. Op-amps have very high input impedance.
Exam Tip
Op-amp input impedance = Very high. Remember: Op-amps have very high input impedance (megohms) so they don't load the signal source. This contrasts with their very low output impedance.
Memory Aid
**O**p-amp **I**nput = **M**egohms (think 'OI = M' = Op-amp Input = Megohms, very high)
Real-World Example
You're using an op-amp to measure a voltage from a high-impedance sensor. The op-amp's very high input impedance (maybe 10 megohms) means it draws virtually no current from the sensor, so it doesn't affect the sensor's output voltage. This allows accurate voltage measurements without loading down the source circuit.
Source & Coverage
Question Pool: 2024-2028 Question Pool
Subelement: E7G
Reference: FCC Part 97.3
Key Concepts
Verified Content
Question from the official FCC Extra Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the E7G topic.