Analog and electronic circuits

In an inverting amplifier using an ideal op-amp, with input resistor Ri = 10 kΩ and feedback resistor Rf = 100 kΩ, what is the voltage gain?

  1. A+11
  2. B−0.1
  3. C−10
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Answer: C. −10

The voltage gain of an inverting amplifier is −Rf / Ri = −100 kΩ / 10 kΩ = −10. The minus sign means the output is inverted relative to the input. +11 is the gain (1 + Rf / Ri) of a non-inverting amplifier built with the same resistors.

Inverting amplifier with an op-amp − + Vin Ri Rf Vout Vout = −(Rf / Ri) × Vin The virtual short keeps the − input near 0 V
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