Question
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?
Answer Options
- A) 1
- B) 0.03
- C) 38
- D) 76
Correct Answer: C
Explanation
The voltage gain of the inverting operational amplifier circuit in Figure E7-3 is determined solely by the ratio of the feedback resistor (R_F) to the input resistor (R_1). We must ensure both resistances are in the same unit (ohms) before calculating the ratio.
R_1 = 1,800 \Omega and R_F = 68 \text{ k}\Omega = 68,000 \Omega. The absolute voltage gain is |A_V| = R_F / R_1 = 68,000 \Omega / 1,800 \Omega \approx \mathbf{37.78}. Rounding to two significant figures, the expected absolute gain is 38. The phase of the signal is inverted, but the magnitude of the voltage is amplified by 38.
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