What voltage gain can be expected from the circuit in Figure E73 when R1 is 10 ohms and RF is 470 ohms?
Why Figure E7-3 is the standard inverting op-amp stage, where the closed-loop voltage gain magnitude is set entirely by the external resistors: gain = RF/R1. With RF = 470 ohms and R1 = 10 ohms, 470/10 = 47. The ideal op-amp assumption (infinite open-loop gain, no input current) forces the inverting input to a virtual ground, so the same current flows through R1 and RF, making the ratio the gain.
Watch out The choice of 0.21 is the reciprocal, R1/RF, which is what you get if you flip the ratio; 4700 is the product of the two resistors, not a ratio.
Feedback over input: RF/R1. Big feedback resistor means big gain.