Based on the circuit information, the value of Rf is

Based on the circuit information, the value of Rf is

• A. 5 kΩ
• B. 50 kΩ
• C. 500 Ω
• D. 50 Ω

Answer: (B)

In an op-amp circuit, the feedback resistor sets the closed-loop gain. In the common inverting configuration, the magnitude of the gain is determined by the ratio Rf/Rin. So, if the input resistor is 5 kΩ and the circuit is designed for a gain of 10 (inverting), the feedback resistor must be 10 times Rin, giving Rf = 10 × 5 kΩ = 50 kΩ. That yields a gain of -Rf/Rin = -50 kΩ / 5 kΩ = -10, which matches the intended amplification. Choosing 50 kΩ fits because the other options would produce much smaller gains: 5 kΩ would give a gain of -1, 500 Ω would give -0.1, and 50 Ω would give -0.01, none of which meet the desired amplification.

In an op-amp circuit, the feedback resistor sets the closed-loop gain. In the common inverting configuration, the magnitude of the gain is determined by the ratio Rf/Rin. So, if the input resistor is 5 kΩ and the circuit is designed for a gain of 10 (inverting), the feedback resistor must be 10 times Rin, giving Rf = 10 × 5 kΩ = 50 kΩ. That yields a gain of -Rf/Rin = -50 kΩ / 5 kΩ = -10, which matches the intended amplification.

Choosing 50 kΩ fits because the other options would produce much smaller gains: 5 kΩ would give a gain of -1, 500 Ω would give -0.1, and 50 Ω would give -0.01, none of which meet the desired amplification.