"Ultimate Electronics Book" - Page 1
Forum section: electronics / beginners

author: hamster_nz
author_rank: Super Contributor
timestamp: June 11, 2020, 04:23:05 am
content: I was just thinking about how frustrated I am with the lumped element model. Sure it works in the simple cases, but hobby electronics can now include such stuff as 2.4GHz RF, and 1.5Gb/s signals, where wires are no longer just wires and PCBs can act like passive components and transmission lines.To model this stuff have to keep shoving in more elements till you get to your needed level of sophistication, but the hard bit is knowing when you need to refine your models.So as a bit of a laugh I typed in "Electronics below the lumped element model" and this popped up:https://ultimateelectronicsbook.com/Oh my... it is like Electronics for the insanely curious.How's this for an introduction to resistance, about 10 paragraphs before V=IR is even introduced:QuoteThat has even made a silly though of mine clearly wrong... that electrons in a resistor move at a constant speed, regardless of where they are. Of course they don't have more kinetic energy at the higher voltage. D'oh.Shame that only "1. CONCEPTUAL FOUNDATIONS OF ENGINEERING" and "2. LINEAR DIRECT CURRENT (DC) ELECTRONICS" have been published.

author: aneevuser
author_rank: Frequent Contributor
timestamp: June 11, 2020, 09:10:44 am
content: Bear in mind that your quoted text is a very classical description of the mechanism of resistance - electrons don't really barrel through a metal like bowling balls, bouncing off atoms as they go. The mechanism of resistance is these days explained by quantum mechanics, where an electron "wave" exchanges energy with the conductor via various scattering events - in fact, IIRC, the dominant mechanism of energy exchange at highish temperatures is via electron-phonon scattering, a phonon being roughly like a quantum mechanical version of a sound wave - a quantised travelling wave, if you like.So bizarrely in fact, resistance arises mainly from the interaction of one type of wave (the electron "wave") with another (the phonon "wave"), rather than from one type of particle bashing into another type of particle.

author: tggzzz
author_rank: Super Contributor
timestamp: June 11, 2020, 10:44:09 am
content: Rule of thumb which works surprisingly well: ignore any product where the name contains "Royal" or "DeLuxe" or "Ultimate".

author: pwlps
author_rank: Frequent Contributor
timestamp: June 11, 2020, 12:05:52 pm
content: Quote from: aneevuser on June 11, 2020, 09:10:44 amThis classical description correspond to the Drude model :https://en.wikipedia.org/wiki/Drude_modelIt is classical but sufficient for "normal" conductors like copper.QuoteActually even quantum models use, most of the time, the so-called "relaxation time approximation" which in fact is almost equivalent to the classical Drude model. This model works relatively well for "normal" metals. However more complete quantum calculations are necessary for some exotic conductors, e.g. the materials used in Peltier-cells used for thermoelectric cooling. But these quantum calculations are actually very difficult (the electron-electron interaction is difficult to model exactly even though recent DMFT techniques improved a lot) and there are no any standard formulas. At the end, for an engineer working with copper cables the classical picture is fairly sufficient.

author: Bassman59
author_rank: Super Contributor
timestamp: June 13, 2020, 05:10:05 am
content: Quote from: tggzzz on June 11, 2020, 10:44:09 amAlso, "Pro."

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 13, 2020, 08:43:44 am
content: You don't really need any math below ohm's law to do transmission line stuff. You can get there just using the basic voltage-current relationships of inductors, capacitors and resistors, and some basic differential calculus. That can give you the telegraphers equations pretty quickly, and from there you pretty much have what you need to do that design. Even when transmissionlines stop working, you still don't need to know anything like why resistance exists. Maxwells equations don't require understanding why resistance is resistance.Don't get me wrong, it's always good to understand, but if your end goal is doing transmission-line design, you don't need to know these things.

author: tggzzz
author_rank: Super Contributor
timestamp: June 13, 2020, 08:57:51 am
content: Quote from: TheUnnamedNewbie on June 13, 2020, 08:43:44 amTha advantage of understanding "more than you need to know" is that you will understand where the simplified models areand are notvalid.Trivial example: you come across people thinking that V=IR, when in reality that's only true for materials where an R can be defined as V/IWithout understanding that, the V=I diode curve is difficult to comprehend and use.In general simplified models are sufficient when repeating standard activities that are well understood in a new context, e.g. transmission lines minimising reflections. That is good and useful, as evidenced by the existence of simplified models.But when you need to step outside the normal box, knowing more helps, e.g. conductors on PCBs used as filters, or directional couplers, or antennas.