What absolute voltage gain can be expected from the circuit in Figure E7-3 when R1 is 1,800 ohms and RF is 68 kilohms?

Q: What absolute voltage gain can be expected from the circuit in Figure E7-3 when R1 is 1,800 ohms and RF is 68 kilohms?

The correct answer is C: 38. The correct answer is C: 38. For the inverting op-amp circuit in Figure E7-3, the absolute voltage gain is calculated as RF / R1 (the absolute value, ignoring the negative sign for inversion). With R1 = 1,800 ohms and RF = 68 kilohms (68,000 ohms): Gain = RF / R1 = 68,000 / 1,800 = 37.78, which rounds to approximately 38. The absolute gain is 38, meaning the output amplitude is 38 times the input amplitude (but inverted). This is a straightforward calculation: divide the feedback resistor by the input resistor.

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Deep Dive: E7G10

The correct answer is C: 38. For the inverting op-amp circuit in Figure E7-3, the absolute voltage gain is calculated as RF / R1 (the absolute value, ignoring the negative sign for inversion). With R1 = 1,800 ohms and RF = 68 kilohms (68,000 ohms): Gain = RF / R1 = 68,000 / 1,800 = 37.78, which rounds to approximately 38. The absolute gain is 38, meaning the output amplitude is 38 times the input amplitude (but inverted). This is a straightforward calculation: divide the feedback resistor by the input resistor.

Why Other Answers Are Wrong

Option A: Incorrect. Gain of 1 would require RF = R1, but RF (68k) is much larger than R1 (1.8k). Option B: Incorrect. 0.03 would be R1 / RF (1,800 / 68,000), which is the inverse of the correct formula. Option D: Incorrect. 76 would be approximately 2 × 38, suggesting a calculation error or misreading of the resistor values.

Exam Tip

Absolute op-amp gain = RF / R1. Remember: For an inverting op-amp, absolute gain = RF / R1. With RF = 68kΩ and R1 = 1.8kΩ, gain = 68,000 / 1,800 ≈ 38.

Memory Aid

**A**bsolute **G**ain = **R**F / **R**1 (think 'AG = RF/R1' = Absolute Gain = RF divided by R1)

Real-World Example

You're designing an inverting amplifier with R1 = 1.8kΩ and RF = 68kΩ. The absolute voltage gain is 68,000 / 1,800 = 37.78, approximately 38. This means the output amplitude will be 38 times the input amplitude (but inverted in polarity).

Source & Coverage

Question Pool: 2024-2028 Question Pool

Subelement: E7G

Reference: FCC Part 97.3

Key Concepts

Op-amp gain Inverting amplifier Absolute gain RF / R1

Official Pool Source

Question text and answer key are synchronized with the current NCVEC Extra Class pool and mapped to the E7G topic.