It's always nice to see that "simple" things are the most fundamental and confusing at the same time for some people. A very well explained video. Thank you for your videos Professor :)
The author of this tutorial could have easily avoided these errors by simply checking them on a simulation tool -Matlab, MathCAD, or SPICE. Readers should do the same. I always check any analysis with one or two simulation tools before I present any material. The best way to check a circuit analysis, of course is to design a bread board and test the circuit. Great job Dr. Ben Yaakov.
I can't recall any specific examples off hand, but I've always found imprecise explanations of certain phenomenon more problematic than useful. Then when you're quizzed on it, you don't know the answer because if you understand the reality, often the answers don't make sense. Seemed to be a typical thing with some randomly selected online problems for some courses. I have to wonder if the person who made this thought they were making it simpler to understand by ignoring all those pesky details, or if they really just didn't understand what they were talking about. My first impression before you explained was "this is not realistic at all", and I'm glad you agree.
I'd still like to see the answers in the ideal inductor case. Re. the impossibility of the ideal switch interrupting the current: we could suppose a switch construction such that the two conducting parts of the switch that are in contact move away from each other at the speed of light. We can assume the switch is contained in a vacuum etc. I think this would make for an interesting physics exercise!
6:19 I believe one can be more specific and say ~5 times the time constant L/R i.e. 5 (L/R)< Ton (For the inductor to fully charge) Sorry for being pedantic. 😛
Question regarding an earlier post. I have been looking for a schismatic for fluorescent desk lamp which has two 15 watt tubes a choke and NO STARTER. Everything I find has a starter and or an electronic choke. This lamp is a product from LUXO, 1960 vintage. I do not understand with volumes of schismatics available on the internet for this fluorescent light, why I can not find one with no starter. I literally have spent hours looking for his Diagram. Thanks.
if the choke and cap produce at start a high enough voltage for generating plasma the lamp will ignite. In fact, there were (I don't know if still available) some lamps with no filament (which is used to lower the voltage needed for breakdown)
Dear Professor. Of course you are right about all errors in this "tutorial". But I think your explanation on slide 9 is not quite correct. The negative sign for derivative di/dt does not mean that the current is going in opposite direction. It does only mean that current's shape has a negative slope.
AS I was explaining in video, if you consider an initial condition in which there is no current in the inductor, then after switch closure the current is in the direction of di/dt. Thanks for illuminating this.
Sorry but this video (and other videos) to discredit the tutorial is nonsense. The circuit clearly shows the characteristics of a pure inductor, there is no series resistance which you have decided to add for your convenience. Therefore there is no L/R quantity, so your analysis is flawed. At the initial closing of the switch, t = 0, electric current starts to flow through the coil thereby producing a magnetic field. The growth in current through the coil from 0 to Imax is not an instantaneous step change, shown in the middle graph, as the incremental change in current through the coil causes an emf to be induced in itself because of this changing magnetic field which opposes and controls the rate of current change (Lenz's Law). This self-induced emf is of opposite polarity to the applied voltage from the battery. Hence the negative sign in the equation -Ldi/dt demonstarted by the bottom graph graph. Eventually steady-state conditions apply, the coil acts as a simple piece of wire, maximum current flows from the battery source, and the self-induced back emf decreases to zero. All shown graphically with no resistance. Opening of the switch has the reverse effects. Then the tutorial and explanation is valid and correct with no added resistance.
Well, Well Well, Electronics Tutorials. You obviously did not bother to watch, study or understand my video. 1. “The circuit clearly shows the characteristics of a pure inductor, there is no series resistance” ??? The fact that the current reaches a fixed value means that there is a resistance. 2. “Eventually steady-state conditions apply, the coil acts as a simple piece of wire, maximum current flows from the battery source,” ??? What the heck is “the coils acts as a piece of wire”? What the heck is “maximum current flows from the battery source“? Is the “simple piece of wire” with no resistance? Then the current will continue increasing. Non zero resistance? Here is your resistor. 3. “Opening of the switch has the reverse effects.”??? Opening the switch causes the current to drop at a constant slope? This is the worst nonsense of all. So why there is a need to protect coils when turned off? You obviously have no experience whatsoever in electrical engineering. Unless you retract, I will prepare another video on the many ignorant assertions in your response.
what!?? what steady state if there is no resistance? May I suggest you read a "real" textbook on basic circuit theory before writing any "tutorial" on internet.
Sam doesn't need my help defending his explanation, but I can't stop myself. Think about what you just said, Electronics Tutorials. Have you studied calculus at all? Think about Vl = L*dI/dt. Do your KVL. Vbat - L*dI/dt = 0 for the case of no resistor. Vbat/L = dI/dt. Since Vbat and L are assumed constant, then dI/dt is also constant, meaning it does not change. the 'd' in dI/dt is to remind us of "delta". ΔI/Δt = Vbat/L . ΔI = (I_t2 - I_t1), Δt = t2-t1 .. So (I_t2-I_t1)/(t2-t1) .. Where have we seen this form before? Oh right, that's our slope for the line formula, m = (y2-y1)/(x2-x1). y=m*x+b, with m = dI/dt. So, if m is constant, does y = m*x+0 (we assume we start from 0 current so b is 0) ever turn? Try plotting it. Tell me if it ever stops increasing. Put it into wolfram alpha, or a calculator. Try increasing x, (which is time, y is current as a function of time) higher and higher. Does the function ever stop increasing? When does it plateau? Because this is the basic expression for a DC voltage source in series with an inductor without resistance. Your statements unfortunately show a lack of understanding for the fundamental mathematics we use in analysis, putting aside understanding of electrical components. I also think you might not be realizing that there is no discrete resistor component, and that one is not required in order to have resistance. Wire has resistance (let's ignore superconductors as they are not unfortunately not practical in typical electrical applications). Inductors are made up of coils of wire. Those wires have resistance, therefore it is an integral part of the inductor construction itself. It is unavoidable. We cannot physically create an inductor without resistance.If you physically measure a /real/ physical inductor with no added resistor, you will find the model I described lies to you. It needs another term. That term is R for resistance. Of course, every circuit has parasitics. Your capacitors contribute to inductance, so we reduce lead spacing. EMC capacitors are very small and placed just so to reduce loop size or they will generate more parasitic inductance. Capacitors have an ESR among other parasitics as well that is very important to consider in circuit design. Resistors have parasitic capacitance and contribute to inductance as well by forming part of a loop (and circuits are loops, hence the name). It is key to understand that we really can't separate the three circuit component models from each other in the real world. We sometimes or often choose to ignore them when they do not significantly impact the purpose/performance of the circuit vs the model, but they're still there. You don't need to have a device titled an "inductor" to have inductance, you don't need a device titled a "resistor" to have resistance, and you don't need a device titled a "capacitor" to have capacitance. These names are simply to tell you what circuit behavior is intentionally emphasized in the design of the component. Anyway, hopefully I didn't say anything inaccurate. I'm also willing to learn and correct myself if I did.
