Notes:
It has been my experience that students require much practice with circuit analysis to become proficient. To this end, instructors usually provide their students with lots of practice problems to work through, and provide answers for students to check their work against. While this approach makes students proficient in circuit theory, it fails to fully educate them.
Students don't just need mathematical practice. They also need real, hands-on practice building circuits and using test equipment. So, I suggest the following alternative approach: students should build their own "practice problems" with real components, and try to mathematically predict the various voltage and current values. This way, the mathematical theory "comes alive," and students gain practical proficiency they wouldn't gain merely by solving equations.
Another reason for following this method of practice is to teach students scientific method: the process of testing a hypothesis (in this case, mathematical predictions) by performing a real experiment. Students will also develop real troubleshooting skills as they occasionally make circuit construction errors.
Spend a few moments of time with your class to review some of the "rules" for building circuits before they begin. Discuss these issues with your students in the same Socratic manner you would normally discuss the worksheet questions, rather than simply telling them what they should and should not do. I never cease to be amazed at how poorly students grasp instructions when presented in a typical lecture (instructor monologue) format!
A note to those instructors who may complain about the "wasted" time required to have students build real circuits instead of just mathematically analyzing theoretical circuits:
                    What is the purpose of students taking your course?
If your students will be working with real circuits, then they should learn on real circuits whenever possible. If your goal is to educate theoretical physicists, then stick with abstract analysis, by all means! But most of us plan for our students to do something in the real world with the education we give them. The "wasted" time spent building real circuits will pay huge dividends when it comes time for them to apply their knowledge to practical problems.
Furthermore, having students build their own practice problems teaches them how to perform primary research, thus empowering them to continue their electrical/electronics education autonomously.
In most sciences, realistic experiments are much more difficult and expensive to set up than electrical circuits. Nuclear physics, biology, geology, and chemistry professors would just love to be able to have their students apply advanced mathematics to real experiments posing no safety hazard and costing less than a textbook. They can't, but you can. Exploit the convenience inherent to your science, and get those students of yours practicing their math on lots of real circuits!

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Notes:
This is a very important concept for students to grasp, especially before they proceed to study operational amplifiers, which are nothing more than differential amplifiers with extremely high voltage gains.

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Notes:
The concept of a "transfer function" is very useful, and this may be your students' first exposure to the idea. It is a phrase used quite often in engineering applications, and may denote an equation, a table of numbers, or a graph.
In this particular question, it is important that students know how to derive and use the basic transfer function for a differential amplifier. Challenge your students to express this function in a more general form, so that calculations may be made with different open-loop voltage gains.

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Notes:
This question is a basic review of an ideal differential amplifier's function. Ask your students what voltage must be "dialed up" at the potentiometer to produce 0 volts at the output of the op-amp for several different voltages at the other input. If they don't understand at first, they soon will after discussing these alternate scenarios.

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Notes:
Obviously, there are limitations to the op-amp formula for calculating output voltage, given input voltages and open-loop voltage gain. Students need to realize the practical limits of an op-amp's output voltage range, and what sets those limits.

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What variable is being stabilized by negative feedback?

Output voltage.

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How is the feedback taking place (step by step)?

When output voltage rises, the system takes action to drop more voltage internally, leaving less for the output.

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What would the system's response be like if negative feedback were not present?

Without negative feedback, the output voltage would rise and fall directly with the input voltage, and inversely with the load current.

Notes:
It is difficult to overstate the importance of grasping negative feedback in the study of electronics. So many different types of systems depend on it for their operation that it cannot be omitted from any serious electronics curriculum. Yet I see many textbooks fail to explore this principle in adequate depth, or discuss it in a mathematical sense only where students are likely to miss the basic concept because they will be too focused on solving the equations.

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Notes:
The significant point of this question is that students see the over-all voltage gain of the opamp radically attenuated from 100,000 to approximately 1. What is not so evident is just how stable this new voltage gain is, which is one of the purposes for employing negative feedback.

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Notes:
Work with your students to calculate a few example scenarios, with the old open-loop gain versus the new open-loop gain. Have the students validate their conclusions with numbers!
Negative feedback is an extremely useful engineering principle, and one that allows us to build very precise amplifiers using imprecise components. Credit for this idea goes to Harold Black, an electrical engineer, in 1920's. Mr. Black was looking for a way to improve the linearity and stability of amplifiers in telephone systems, and (as legend has it) the idea came to him in a flash of insight as he was commuting on a ferry boat.
An interesting historical side-note is that Black's 1928 patent application was initially rejected on the grounds that he was trying to submit a perpetual motion device! The concept of negative feedback in an amplifier circuit was so contrary to established engineering thought at the time, that Black experienced significant resistance to the idea within the engineering community. The United States patent office, on the other hand, was inundated with fraudulent "perpetual motion" claims, and so dismissed Black's invention at first sight.

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Vin       Vout       0 volts       0 volts       +5 volts       +5 volts       +10 volts       +10 volts       +15 volts       +15 volts       +20 volts       +15 volts       -5 volts       -5 volts       -10 volts       -10 volts       -15 volts       -15 volts       -20 volts       -15 volts

Notes:
A common mistake I see students new to opamps make is assuming that the output voltage will magically attain whatever value the gain equation predicts, with no regard for power supply rail voltage limits.
Another good follow-up question to ask your students is this: "How much voltage is there between the two input terminals in each of the situations described in the table?" They will find that the "golden rule" of closed-loop opamp circuits can be violated!
If students have difficulty answering the follow-up question, drop these two hints: (1) Rail-to-rail output swing and (2) Latch-up.

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Notes:
I have found that some students have difficulty with the terms "heavy" and "light" in reference to load characteristics. That a "heavy" load would have very few ohms of impedance, and a "light" load would have many ohms of impedance seems counter-intuitive to some. It all makes sense, though, once students realize the terms "heavy" and "light" refer to the amount of current drawn by the respective loads.
Ask your students to explain why the straight piece of wire fails to "buffer" the voltage signal in the same way the the opamp follower circuit does.

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Notes:
Ask your students to explain why there will be (practically) no voltage between the input terminals of an operational amplifier when it is used in a negative feedback circuit.

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Magnitude of input terminal currents: infinitesimal

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Input impedance: infinite

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Output impedance: infinitesimal

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Input voltage range: never exceeding +V/-V

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Output voltage range: never exceeding +V/-V

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Differential voltage (between input terminals) with negative feedback: infinitesimal

Notes:
Just in case your students are unfamiliar with the words infinite and infinitesimal, tell them they simply mean "bigger than big" and ßmaller than small", respectively.

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Notes:
Knowing where to check for critical signals in a circuit is an important skill, because it usually means the difference between efficiently locating a fault and wasting time. Ask your students to explain in detail the rationale behind checking for voltage across the capacitor, and (again, in detail) what certain voltage measurements at that point would prove about the nature of the fault.

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Notes:
This is one of my favorite questions to ask students as they begin to learn how negative feedback works. It is an excellent "litmus test" for comprehension of negative feedback: those students who understand how and why negative feedback works will immediately grasp the significance of the modified feedback connection; those who do not understand negative feedback will fail to grasp why this circuit works at all. Spend as much time as you need discussing this circuit, because it holds the key to student understanding of a great many opamp circuits!

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Transformer T₁ primary winding fails open: Output voltage falls to zero after filter capacitors C₁ and C₂ discharge.

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Rectifying diode D₃ fails open: No effect seen at no load, regulation falters sooner as load gets heavier.

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Rectifying diode D₄ fails shorted: Fuse may blow, diode D₂ may fail due to overheating (and quickly blow the fuse if it also fails shorted).

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Resistor R₁ fails open: Output voltage falls to zero after filter capacitor C₂ discharges.

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Zener diode D₅ fails open: Output voltage rises to nearly full (unregulated) value.

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Operational amplifier U₁ fails with output saturated positive: Output voltage rises to nearly full (unregulated) value.

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Transistor Q₁ fails open (collector-to-emitter): Output voltage falls to zero after filter capacitor C₂ discharges.

Notes:
The purpose of this question is to approach the domain of circuit troubleshooting from a perspective of knowing what the fault is, rather than only knowing what the symptoms are. Although this is not necessarily a realistic perspective, it helps students build the foundational knowledge necessary to diagnose a faulted circuit from empirical data. Questions such as this should be followed (eventually) by other questions asking students to identify likely faults based on measurements.

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Opamp (U₁) failed with output saturated negative.

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Zener diode (D₁) failed shorted.

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Resistor R₁ failed open.

Notes:
Ask your students to explain their reasoning, as to why they chose the component faults that they did. Also, ask them to identify any components they think are working properly (beyond a doubt).

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Notes:
This circuit is not only worthwhile to discuss with your students as an example of negative feedback in action, but it is also practical for them to use as an impromptu power supply ßplitter" when only a single supply is available. If you do decide to build this circuit, be careful of the transistors' power dissipations! Determine the maximum imbalance current to the load (how much current will be drawn through the Ground terminal), and then multiply that current by +V (or -V, absolute). This will be the maximum power dissipation value either transistor may have to safely handle.
In response to the challenge question, the wisdom of the bypass capacitors will be evident if a pulsating load (such as a brush-type DC motor) is placed between either "rail" and Ground. The opamp must swing its output back and forth very rapidly to turn on each transistor fast enough to counter dips in voltage caused by the pulsating load. Capacitors naturally resist change in voltage, and so are ideal for mitigating such voltage dips, easing the burden placed on the opamp.

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Notes:
This simple filtered voltage divider circuit works well when the current draws are low, or at least very close to being equal, on the +V and -V load rails. It does not work so well for highly asymmetrical loads, or where low quiescent current draw is important (low-power battery circuits, for example). In applications requiring better +V/-V voltage stability, an opamp "follower" circuit is recommended after the voltage divider.

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Notes:
Much could be said about good amplifier circuit design in this question, but the fundamental point is for students to see how negative feedback coupled with the extremely high gain of the opamp minimizes crossover distortion. Be sure to focus students' attention on that point until they understand it well before launching into a discussion about the finer points of amplifier design.
It should be noted that this solution to crossover distortion in a push-pull amplifier circuit does not always yield the best results. In order for the opamp to ensure a smooth transition between half-cycles, its output must jump about 1.4 volts instantaneously to go from turning one transistor off to turning the other transistor on. Of course, no opamp can do this, because all have slew rate limitations. So, there will still be some crossover distortion, but not nearly as much as without the opamp (and with far less quiescent power dissipation that the two-diode solution!).

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Notes:
Guarding is a technique used in many test and measurement scenarios, and it serves as a great example of opamps used as voltage followers.
If students are not convinced of the seriousness of cable capacitance in an application such as the one described, suggest these values to them and ask them to calculate the cutoff frequency of the low-pass filter formed by R_signal and C_cable:

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R_signal = 20 MW

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C_cable = 175 pF

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Notes:
A simple voltage buffer circuit is the easiest context in which to understand the function of a bias current compensating resistor, and so it is presented here to allow students to see its impact.

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