Operational Amplifiers: Principles and Applications Quiz Quiz

Explore essential concepts in operational amplifier functionality, configurations, and real-world applications. This quiz covers topics such as op-amp characteristics, feedback mechanisms, and common circuit implementations, helping electronics enthusiasts and students reinforce their understanding of operational amplifiers.

1. Ideal Op-Amp Characteristics

   Which of the following is a characteristic of an ideal operational amplifier (op-amp) in a typical circuit analysis scenario?

   1. Low input impedance
   2. Significant input current
   3. Infinite open-loop gain
   4. High output impedance

   Explanation: An ideal op-amp is modeled with infinite open-loop gain, allowing it to amplify input differences to any level controlled by feedback. In contrast, significant input current and low input impedance are not ideal; an ideal op-amp has infinite input impedance, so it draws virtually no current. High output impedance is a disadvantage, while an ideal op-amp should have zero output impedance for maximum power transfer. Only infinite open-loop gain describes the ideal characteristic here.

2. Inverting Amplifier Gain Calculation

   In an inverting amplifier circuit using an op-amp, if the input resistor is 2 kΩ and the feedback resistor is 8 kΩ, what is the voltage gain of the circuit?

   1. 4
   2. 0.25
   3. -0.25
   4. -4

   Explanation: The voltage gain of an inverting amplifier is the negative ratio of the feedback resistor to the input resistor, so -8 kΩ / 2 kΩ equals -4. The positive values 4 and 0.25 are incorrect because they ignore the sign and the ratio. Option -0.25 is a common numerical error made by inverting the division order. The correct gain, taking both magnitude and sign into account, is -4.

3. Comparator Function Example

   When an op-amp is used as a comparator and the non-inverting input receives a higher voltage than the inverting input, what is the likely output state (assuming dual supplies)?

   1. Output remains at zero volts
   2. Output is halfway between positive and negative supply
   3. Output saturates to the positive supply voltage
   4. Output follows the inverting input

   Explanation: As a comparator, an op-amp outputs its maximum positive voltage when the non-inverting input is higher than the inverting one. Staying at zero volts or following the inverting input misconstrues op-amp operation in comparator mode. The output typically saturates to supply rails rather than a midpoint. Thus, the first option accurately describes comparator behavior under these conditions.

4. Effect of Negative Feedback

   How does applying negative feedback to an operational amplifier influence its performance in linear applications?

   1. It stabilizes gain and increases linearity
   2. It reduces bandwidth significantly
   3. It decreases input impedance sharply
   4. It causes the output to oscillate

   Explanation: Negative feedback in op-amp circuits ensures stable, predictable gain and improves linearity by correcting output deviations. It generally increases, not decreases, input impedance and maintains or broadens bandwidth instead of reducing it dramatically. Rather than causing oscillations, negative feedback actually helps prevent them, making the first option correct.

5. Op-Amp Integrator Output

   In an ideal op-amp integrator with a constant positive voltage applied to the input, what happens to the output voltage over time?

   1. The output voltage stays constant
   2. The output voltage decreases linearly
   3. The output voltage increases linearly
   4. The output voltage oscillates sinusoidally

   Explanation: An ideal op-amp integrator inverts and accumulates the input; applying a constant positive voltage causes the output to decrease linearly over time. Linear increase is incorrect since it ignores the inversion characteristic of the circuit. Constant or oscillating outputs would not result from a constant DC input in an ideal integrator. Therefore, a linear decrease is the correct description.