Question E7G10:
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?  

Choices:  
A: 1  
B: 0.03  
C: 38  
D: 76    

Correct Answer is  C: 38  

Answer: 38

Why it’s correct:
- Figure E7-3 is an inverting op-amp amplifier. For an inverting amplifier, the voltage gain is
  $$A_v = -\frac{R_F}{R_1}$$
  The question asks for absolute gain, so use the magnitude:
  $$|A_v| = \frac{R_F}{R_1} = \frac{68\,\text{k}\Omega}{1.8\,\text{k}\Omega} = \frac{68{,}000}{1{,}800} \approx 37.78 \approx 38$$

Why the other choices are incorrect:
- A: 1  
  - Would be true for a voltage follower (non-inverting with unity gain), not for this inverting configuration with large feedback ratio.
- B: 0.03  
  - This is the inverse ratio, $R_1/R_F \approx 1{,}800/68{,}000 \approx 0.0265 \approx 0.03$, which is not the gain of the inverting amplifier.
- D: 76  
  - Not applicable. For non-inverting you’d have $1 + R_F/R_1 \approx 39$, not 76. This choice likely comes from an incorrect doubling or misreading of the formula.

Useful formulas and rules of thumb:
- Inverting op-amp gain: $$A_v = -\frac{R_F}{R_{\text{in}}}$$
- Absolute (magnitude) gain: $$|A_v| = \frac{R_F}{R_{\text{in}}}$$
- Non-inverting op-amp gain (for comparison): $$A_v = 1 + \frac{R_F}{R_{\text{g}}}$$
- “Absolute gain” means ignore the minus sign (phase inversion).