# Circuit Theory 2014 May – Teaching Summaries

I start writing summaries for my daily teaching in UTAR and posted them in our dedicated Facebook group.

I not really sure if the students will appreciate the summaries. But I do think* that they can use the summaries to recap what have been delivered in that the class while they are asleep. To me, these summaries can re-explain and re-clarify some concepts, which I have badly explained in class.

Week 1
Monday :
Summary of L1 Lecture Group (Monday).
Today I have introduced about myself and also brief the course assessment and the OBE. Students should have a rough idea about the lecturers’ expectation and some important timeline. Also, we have learned that coulomb is just a unit to measure a group of electrons. However, the reason for not measuring the electrons in “1k” or “10k” is not explained, and I will leave it as self-study.

We also learned how to look at the voltage source — the positive terminal is just the place full of positive charge and negative terminal is the place that lack of positive charge (I used the term “many positive charges and little charges, though). We also learned how to measure the voltage source with the reversed polarity V. Also, the Ohm’s law — the “law” is not always correct. It can be violated when the condition changes. In fact, the physics’ law remains as a law as long as some proved it is wrong. Best example is the Newton’s laws of motion. On the other hand, the mathematics theorem is a much more rigorous than Physics’ law. A mathematics’ theorem remains theorems until human logic is found wrong (which is a disaster).

As for the video sharing section — the speed dating of the engineer Khai. I hope the students learned that, whether engineering is a boring or interesting subject (we make things happen!!) — it all depends how you see it. Engineer is an artist when he/she see things beautifully.

Week 1 Wednesday L1 Summary.
Today, we have learned that voltage (potential different) requires two points for the value to make sense. And, ground is just a reference of 0v. Placing ground at different location will influence the Vx (nodal voltage) but has no influence to the voltage across component (e.g. Vab). The notion of open circuit and closed circuit has been discussed with a short question to test students understanding. Majority of students has grabbed the concept correctly. It is okay to make mistake in the class, rather than making mistake during the final examination. The class ends with a conjecture of a man swinging over the transmission line – to demonstrate the idea of electric shock.

Week 2  Monday L1 Summary

As discussed in the class, I have to change the Week 3 Monday (9-June-2014) lecture to 4-5pm due to an important meeting. I have also reminded the students about the new mid term test and the lab 2 re-registration. At the same time, I also promoted the Counselling Wellness Week 2014.

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We have learned many things in today’s two hours lecture.

Our discussion on power equation is only limited to the case of passive element, and we will move to the power supply/absorb by the active element after the page 40++.  Students have showed confusion about the absorbing and receiving power. Again, it is okay to make mistake in class.

Student may be confused about the “reference direction” of the current flow. We will look into this issue later through many examples in class.

Also, we have learned the concept of ideal voltage and current source — the ideal voltage source will preserve the potential difference (voltage) no matter how we connect the port (A and B). However, I also show the example of how this statement can be invalidated, that is by short circuiting A and B. The same concept (but different method) applies to ideal current source.

We also learned the practical voltage and current source and the source conversion without discussing the equations in detail. We will revisit these equations once we have studied the KVL, KCL, voltage divider and current divider rule, that is after page 40++.

Week 2 L1 Wednesday Summary.

Today we have learned the KVL and KCL with a few examples on the whiteboard and slides. Also before the class end, we have seen a circuit that is logically wrong in the context of KCL. I hope the message is clear — the KVL and KCL are the fundamental laws in circuit theory. A logically correct circuit should always obey the KVL and KCL (at most of the time). I guess everyone* has fun in guessing the logically incorrect circuit.

Today is also the second time where I need deliver the lecture without mic. It isn’t a bad day as someone said I look like 20++. 😀 ~~  Okay, that is a guy who say so.  -_-

And, the next Monday class start at 5pm. See ya.

Pre-Course Survey Result.

About 50% of students have taken this survey. Majority of them are Year 1 and 2 students and they have taken the UTAR foundation. 93% of the students have scored at least C in the last mathematics subject. 40% of them scored A. About 21% of the students will read through the slides before the lecture and about 54% of them will try the tutorial at best effort.

Week 3 Monday L1 Summary

The class starts at 5pm as I have important research meeting at 3-5pm.

Today, we have learned the voltage divider rule and current divider rule. The equation of the voltage divider rule is easy to memorize as it looks like the “ratio” of the voltage that divider by the resistors R1 and R2. Meanwhile, the current divider rule is similar to voltage divider rule, but it takes the “opposite” resistor as the numerator. We have gone through the derivation of voltage divider rule but I will leave the derivation of the current divider rule as exercise.

One student asked how to apply current divider rule in a circuit of three resistors in parallel. Some textbooks has the trick/shortcut to solve it. To me, I will prefer to solve it with KISS (Keep It Simple, S**) principle. I will combine the three resistors to two before applying the current divider rule.
I realize that many of the students are still confused in the lecture. Perhaps it is due to my boring lecture. Perhaps the “numbers” starts disappearing in the given examples. To avoid avalanche breakdown, students are advised to talk to friends, refer to text books or talk to the lecturer. At the same time, I will try* to show more examples (with numbers) in class.

Week 3 Wednesday L1 Summary
Today, we studied the example given by Alex Ah Boon — resistors network with a “short-circuit” line. By redrawing the circuit, it is easy to see that the circuit is actually a couple of series and parallel connected components.

Next, we have gone through the Delta-Y transformation. I have explained an easy way to remember all the equations. Then, we went through the example in the slide — to find the equivalent resistance of a circuit of neither parallel nor series connection. As long as we apply the Delta-Y (or Y-Delta) transformation at the correct components, the question can be easily solved.

We have finished the Chapter 1 and will proceed to Chapter 2 – Circuit Theorems in the next week. The students are advised to have gone through the slides before the lecture.

Also, the tutorial will be started next week (Week 4). Students are advised to attempt all the tutorial questions before the class.
Also, the online quiz will be uploaded on Week 4 Wednesday, 8pm. You are given 3 hours to solve the online quiz. The detail of the online quiz will be uploaded later.

Week 4 Monday L1 Summary

Today, we have entered the Chapter 2. Basically, the Chapter 2 is about the systematic ways to solve/analyse the circuit with KVL and KCL.

We applied branch-current analysis and mesh analysis to analyse the example in the slide, i.e. the circuit that consists of two voltage sources. We have learned that the branch current analysis is no more than just forming bundle of KVL and KCL equations. And the mesh analysis is just forming KVL equations (the loop). As long as we have “sufficient equations”, the branch current/voltage can be found with linear algebra. Because everything is about KVL and KCL, we learned that violating “steps” (e.g. change the loop direction, current direction, etc) will not change the answer as long as the equations we form fulfil KVL and KCL.

By comparing the equations forming from branch current analysis and mesh analysis, the students are able to tell that branch current analysis imposes more equations than mesh analysis. Personally, I seldom use branch current analysis but I do think that branch current analysis is a fundamental method, where it explains (almost) everything inside the mesh (and nodal) analysis.

Today’s video sharing session is about the life of Tesla. I mentioned something about the current war between Edison and Tesla. Hopefully, it does inspire the students a little bit.

This Wednesday, we will proceed with nodal analysis and the learning the calculators.

Week 4 Wednesday L1 Summary.

Today, we have learned how to use the Casio calculator to solve 3×3 matrix. We learned how to use  the nodal analysis to solve the same example we used in branch-current analysis and mesh analysis. Also, a simple example have be given in the lecture to test the student understanding. Though nodal analysis forms lesser equations (*depends situation) than mesh analysis, many students still think mesh analysis is easier. Personally, I prefer to solve the circuit problem with nodal analysis — perhaps it is because I always solve the equations with computer instead of calculator.

Next week we will proceed with more details in mesh and nodal analysis — the super mesh and super node.

Week 5 Monday – No class. Sick.

Week 5 Wednesday L1 Summary.

We learned the concept of super-mesh from the modified version of example that used in branch current analysis (BCA). Note that I only modify the voltage source to current source. The reason I use back the BCA example because I believe the students are much more easy to learn with the familiar example.

Next week, I intend to guide them through the example in the slide — the one that has resistor and current source in the middle. I believe this is a good example for them to learn supermesh as well.

Plan for replacement for lecture on Week 6 Friday afternoon. I believe this will be the best time for all.

Week 6 Monday

Today we learned the super node analysis. Then, we go into the chapter 3 and learn the superposition theorem. However, the example that we learn today is quite simple. In later time, dependent source will be appear intensively in the example. And, this will be a good time for us to learn how to deal with dependent sources.

We have decided that week 7 Monday we have 3 hour class. Not for week 8 as some of them have exam.

Week 6 Wednesday

Today the students request to teach the Thevnin’s theorem first as the assignment due next week Friday. So, I have explain two simple Thevenin circuit on the white board. I have shown them what I mean by equivalent.

Some of the students are still confused about the Thevnin’s theorem. Next week Monday we have to re-explain this in detail again.

The projector did not work well today.

Week 7 Monday.

We have 3 hours class today, covering Thevenin’s (normal and special case) and Norton.

May be it is not a good idea to have a 3 hours class as it is tiring.

Week 7 L1 Wednesday Summary

Today we learned the concept of maximum power transfer, with the help of the excel graph. From the graph, students are able to tell Rth=Rload is the condition for maximum power transfer and the circuit must be in “one voltage source Vth series with Rth and series with Rload — that’s why the Thevenin’s theorem is applied in the example. I didn’t go through the derivation to prove Rth=Rload, though I think it is important for those serious learner. In fact there is a crazy question (Q1(b)) in 2011 final paper that challenged the maximum power transfer condition, which I think worth to be mentioned here. It violates the maximum power transfer condition in a tricky way.

Today, I also mentioned a Japan drama that worth sharing — “Proposal Daisakusen” as a student just look like him.

By the way, It becomes my habit to wrote down my every teaching activity. Hope you don’t mind.

Week 8 L1 Monday Summary
Today we entered the Chapter 4. In this chapter, we will learn the characteristic, especially on the voltage-current relations of capacitor and inductor.  If we treat the current as the water flow, then the capacitor can be viewed as water tank. The charging and discharging behavior of capacitor are similar to fill in and discharge the water in the water tank. We have learned two important equations about capacitor — the q(t)=c v(t) and the i(t) = c dv(t)/dt. From the equations, we learned that the (a) voltage of the capacitor is a continuous function with respect to time (voltage cannot be changed abruptly); (b) Constant capacitor voltage implies that the capacitor is acting as an open circuit; and (c) the practical capacitor will discharge through air.
We will have 3 hours class on Week 9  Monday and no class on Wednesday. We will discuss this again on the coming Wednesday.
Week 8 L1 Wednesday Summary.
Today we learned how to replace the switch of a circuit with unit step function, u(t). This function is important as we will use it a lot in the later examples. I have demonstrated how to delay (right shift) the unit step function, i.e. u(t-a) with derived equations. A few examples have been demonstrated to construct different kind of square wave with u(t). More sophisticated questions can be found in the tutorial.
A lot of students missing today and one student late for 35 minutes. Most likely they will be confusing when I use unit step function in the coming Monday class. As to discourage such culture, I will refrain myself to re-explain what we have learned today unless they sing in front of us. >:)
Next week Monday we have 3 hours class. We will learn the step response of the capacitor, i.e. the charging and discharging behavior of the capacitor when the switch is closed (that is where we use u(t) function). This section will be challenging. You are encourage to drink expresso if you plan to sleep in class.

Week 9 Monday L1 Summary.
Today we have learned the followings:
– The charging and discharging voltage of capacitor can be calculated with full response equation, i.e. V_c(t) = V_c(0)e^(-t/tau) + V_c(infinity)(1-e^(-t/tau)), where tau = RC.
– The charging and discharging current of the capacitor can be calculated with I_c = C dV_c / dt (if you good with calculus). Or, with KVL.
– The charging or discharging voltage/current will reach steady state (stabilize) after 5tau.
– The equation to combine parallel capacitors is C1 + C2, while the equation to combine two series capacitors is C1||C2. The equations are opposite to the resistors.
– The inductor will slow down the change of current and the fundamental equation is V_L = L d I_L / dt.
– The charging and discharging current of the inductor can be calculated with full response equation as well, i.e.I_L(t) = I_L(0)e^(-t/tau) + I_L(infinity)(1-e^(-t/tau)), where tau = L/R.
We (L1 lecture group) have no class on this Week 9 Wednesday as I am having training (in campus).
We (L1 lecture group) have no class for the whole Week 10 due to Hari Raya.
We (L1 lecture group) have 3 hours class on Week 11 Monday.
Good luck for your mid term test and see you again on Week 11.

Week 10 Hari Raya. No Class

Week 11 Monday L1 Summary
We spent the first half hour today to discuss the Current War between the Edison and Tesla — the war between DC and AC current. Though it is not a must-learn-topic in the CT class, I find this story interesting and worth to be shared among the students. At least the students know what they are learning for (hopefully -_-).
Before entering the AC analysis, we have to learned the “preliminary mathematics”. We learned how to convert between sin and cosine– it can be done with a lot of mathematics expression or with graphical approach. We also learned how to determine the phase shift between two sinusoids (sin/cosine waves), and determine the leading and lagging.
A phasor is a common mathematical framework to analyze the AC circuit. In fact, phasor is just a complex number, and it is called “phasor” because we are using to analyze the phase of sinusoids. We have learned how to transform from a sinusoid to phasor — to transform a sin wave from time domain to complex domain. Of cause, during the transformation, the frequency (e^{wt}) will be suppressed.
The phasor transformation (okay.. it is my term. We don’t call it “phasor transformation” in textbook) is something similar to Laplace transform. You have a “Table” to memorize”. We will learn the detail of the transformation in the Wednesday class.
Week 11 Wednesday L1 Summary
We can solve a simple AC circuit with capacitor by solving the first order linear equation (if you are good in mathematics).
We learned how to transform a differential equation and integration equation with phasor transformation. With that w can use it to solve some specific type of first order linear equation that consists of sinusoid.

Week 12 Monday L1 Summary
Today we have covered the Chapter 5.3. Phasor transformation changes the AC circuit looks like “DC” (note: not the real DC). To be exact, the phasor transformation transform the circuit from time-domain to complex domain. The inductor and capacitor will become impedance load (something like resistor, but the resistance will change according to frequency). In complex domain (or the fake DC circuit), you can calculate the voltage/current as if everyhing is in DC.
And, remember, you have to convert the sinusoid (time domain) to cosine first before converting it to phasor.
Week 12 L1 Wednesday Summary
We started the Chapter 6 today. The instantaneous power p(t) has been derived in the class. In CT, we not really concern about the instantaneous power. The average power equation is explained in the class.

It is near to the end of the course.

On behalf of all the teaching members, we would like to thank to all of you for joining the class. Hope you have fun for the past 13 weeks.

We apologize sincerely for any mistake made in the class and promise improvement in the future. Therefore, we would like to seek your precious feedback. This helps us to shape how we deliver the material the next time around.

Please do write to us for any suggestion.

Thank you and good luck for final!