What will be the output voltage of the circuit shown in Figure E7-3 if R1 is 1,000 ohms, RF is 10,000 ohms, and 0.23 volts DC is applied to the input?

Q: What will be the output voltage of the circuit shown in Figure E7-3 if R1 is 1,000 ohms, RF is 10,000 ohms, and 0.23 volts DC is applied to the input?

The correct answer is D: -2.3 volts. The correct answer is D: -2.3 volts. For the inverting op-amp circuit in Figure E7-3, the output voltage is calculated as Vout = -(RF / R1) × Vin, where the negative sign indicates inversion. With R1 = 1,000 ohms, RF = 10,000 ohms, and Vin = 0.23 volts DC: Gain = -RF / R1 = -10,000 / 1,000 = -10. Output = -10 × 0.23 = -2.3 volts. The output is inverted (negative) and amplified by a factor of 10. This is the standard calculation for an inverting op-amp: multiply the input by the negative of the gain ratio.

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Deep Dive: E7G09

The correct answer is D: -2.3 volts. For the inverting op-amp circuit in Figure E7-3, the output voltage is calculated as Vout = -(RF / R1) × Vin, where the negative sign indicates inversion. With R1 = 1,000 ohms, RF = 10,000 ohms, and Vin = 0.23 volts DC: Gain = -RF / R1 = -10,000 / 1,000 = -10. Output = -10 × 0.23 = -2.3 volts. The output is inverted (negative) and amplified by a factor of 10. This is the standard calculation for an inverting op-amp: multiply the input by the negative of the gain ratio.

Why Other Answers Are Wrong

Option A: Incorrect. 0.23 volts is just the input voltage, not the output. The output is amplified and inverted. Option B: Incorrect. 2.3 volts would be the output if it weren't inverted, but the inverting amplifier produces a negative output. Option C: Incorrect. -0.23 volts would be the output if the gain were -1, but with RF = 10k and R1 = 1k, the gain is -10.

Exam Tip

Inverting op-amp output = -(RF/R1) × Vin. Remember: For an inverting op-amp, Vout = -(RF/R1) × Vin. With RF=10k, R1=1k, Vin=0.23V: Vout = -10 × 0.23 = -2.3V.

Memory Aid

**I**nverting **O**utput = **N**egative **G**ain × **I**nput (think 'IO = NGI' = Negative Gain × Input)

Real-World Example

You're using an inverting op-amp with R1 = 1kΩ and RF = 10kΩ to amplify a 0.23-volt DC signal. The gain is -10, so the output is -2.3 volts. The negative sign indicates the signal is inverted - a positive input produces a negative output.

Source & Coverage

Question Pool: 2024-2028 Question Pool

Subelement: E7G

Reference: FCC Part 97.3

Key Concepts

Op-amp output Inverting amplifier Voltage calculation DC amplification

Official Pool Source

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