Is power lost in a circuit always lost as heat? - Page 1
Forum section: electronics / beginners

author: wardenclyffe
author_rank: Contributor
timestamp: March 20, 2013, 04:52:42 pm
content: The title pretty much says it all, but I heard someone ask this question the other day and I realized I am not really sure. When we talk about power losses in a circuit are we always referring to how much is lost as heat. In other words, are there other methods for power to be lost in a circuit other than by radiated heat? Noob question for sure.

author: c4757p
author_rank: Super Contributor
timestamp: March 20, 2013, 05:00:44 pm
content: The vast majority, yes. Some can be lost as EM radiation (radio waves, light, etc), and obviously anything motorized can dissipate power as kinetic energy, but unless the circuit is intentionally built to do this, 99.99999% of the energy lost is heat.

author: ftransform
author_rank: Frequent Contributor
timestamp: March 20, 2013, 05:36:08 pm
content: I wish it was lost as muffins...

author: olsenn
author_rank: Frequent Contributor
timestamp: March 20, 2013, 06:03:55 pm
content: I'm curious to know how power dissipated in radio waves is calculated. I still don't quite understand the concepts of VSWR and antennas, but I honestly can't visualize how, or rather what, RF power is?

author: sacherjj
author_rank: Frequent Contributor
timestamp: March 20, 2013, 08:49:00 pm
content: Quote from: olsenn on March 20, 2013, 06:03:55 pmRF power is what is emitted in the form of an electromagnetic wave. This can occur at a variety of frequencies along the spectrum. These are RF at lower frequencies, before they turn into non-visible, then visible, then non-visible lights and on up to xrays and gamma rays, etc.VSWR is a measure of the effectiveness of impedance match between the transmission line and antenna. A good match is like a hallway with completely smooth walls out through the exit. You have all power transfer possible. As your impedance match gets worse, it is like putting a wall at the end with a door that is not the full size of the hallway and instructing those that hit the wall to turn around and walk against the people trying to get out. In addition to lost power, it can cause some issues with signal reflections, etc.

author: olsenn
author_rank: Frequent Contributor
timestamp: March 20, 2013, 08:59:34 pm
content: QuoteI like that analogy, except where is the door? The electrons don't escape the antenna do they? Do they move with great velocity through the base of the antenna up to the tip and then burst right through the tip from their own momentum? How does an ideal transmitter function? What exactly is an electromagnetic wave? If a wave is something that moves periodically, what in an electromagnetic wave moves?

author: c4757p
author_rank: Super Contributor
timestamp: March 20, 2013, 09:11:21 pm
content: I'll skip explaining EM waves, as I'm sure someone else could do it better (my best explanation that I could come up with just ended up being confusing), but as for (V)SWR, impedance, reflection and whatnot, watch this video. It really is excellent.

author: ve7xen
author_rank: Super Contributor
timestamp: March 20, 2013, 09:21:00 pm
content: My confusion about EM radiation has never been (so much) about the wave nature, but about how an antenna couples to the environment to actually radiate energy. Does anyone have a good reference that explains the physics involved and how it relates to Ohm and Kirchhoff etc?

author: ptricks
author_rank: Frequent Contributor
timestamp: March 20, 2013, 10:18:32 pm
content: I don't know if they teach this way now, but 20+ years ago when I was in college we had to know the amount of power the circuit would dissipate in every experiment, we had to figure out where all the power went , we were not allowed to just say the supply was 5V, we had to show it as 5V @ 150ma .It was a good way to understand what was happening in the circuit and served me well later because it taught me to add up what a circuit needed and not supply it with more than that. I think the trend now is just to put a 5V supply on something with the idea of it will only use what it needs, but that is bad if something fails.One of the things to keep in mind about Kirchoffs law is that it has some quirks that need to be understood for working with RF circuits, you might want to read up on Maxwell as he is more relevant for understanding RF power.

author: ignator
author_rank: Regular Contributor
timestamp: March 20, 2013, 10:24:40 pm
content: Quote from: c4757p on March 20, 2013, 09:11:21 pmI thought it was a good analogy. OK, the people are flowing in a resonant cavity, in and out, in and out, with what should be a sine wave flow rate of "electrons", the partial door works but the real problem is this is a resonant cavity, and to maximize the flow, and hence power, you need to think of this flow of electrons in and out of the antenna in this resonant way.OK I'm not doing any better.It's MAGIC. If you can explain what a magnetic field is, and what and electric field is, and what an electron is, then you can intuitively understand this. Heck they can't explain the speed of light, or gravity, or why the traveling of these photons of electromagnetic traveling waves are perpetual motion machines. As well all matter that has propagated through space for the last 13+ billion years.We use Maxwell's equations, Faraday's laws, etc. It just works. Heck one of the posters here has Fourier's transform as his user name, can he see the convolution integral that maps frequency domain to time and back again? I can't, but Laplace and Fourier could.If anyone can provide an intuitive explanation, I'm all ears.

author: IanB
author_rank: Super Contributor
timestamp: March 20, 2013, 10:52:14 pm
content: Quote from: ve7xen on March 20, 2013, 09:21:00 pmA simple thought experiment could provide an analogy. Imagine water in a long closed pipe with a piston at the end, and imagine this piston is connected to a paddle on the surface of a lake. If you move the water back and forth in the pipe in an oscillating manner the piston at the end will move back and forth with the water pressure, which will move the paddle in the lake. The paddle moving in the lake will generate waves in the water that will radiate outwards and carry energy away. No water is actually flowing in this example, neither flowing out of the pipe, nor flowing away from the paddle (waves move through water, but the water stays where it is).It follows that you will have to do work moving the water back and forth in the pipe to provide the energy to move the paddle in the water and generate the waves. We could say that the water in the pipe is coupled to the paddle.There is a similar kind of situation with electromagnetic radiation. The charged electrons moving back and forth in the antenna generate moving electric and magnetic fields, which couple together to form electromagnetic waves carrying energy away from the antenna. By analogy with the water example, you have to do work moving the electrons back and forth to provide the energy carried away by the waves.Physics provides of course a detailed mathematical description of how an antenna behaves that I cannot begin to reproduce, but I often find a conceptual understanding helps me to comprehend the underlying mathematics for something complex like this. It turns it from a jumble of equations into something that begins to have meaning.

author: ignator
author_rank: Regular Contributor
timestamp: March 21, 2013, 12:53:25 am
content: Quote from: IanB on March 20, 2013, 10:52:14 pmThis is a pretty good analogy.

author: c4757p
author_rank: Super Contributor
timestamp: March 21, 2013, 01:01:50 am
content: Quote from: ignator on March 20, 2013, 10:24:40 pmCareful with "they". You'd be surprised how well some of this is understood by many people.

author: c4757p
author_rank: Super Contributor
timestamp: March 21, 2013, 01:03:48 am
content: Quote from: IanB on March 20, 2013, 10:52:14 pmGreat bigto you. That's a good one. Do you teach?

author: BravoV
author_rank: Super Contributor
timestamp: March 21, 2013, 01:07:09 am
content: Quote from: c4757p on March 21, 2013, 01:03:48 am+1, great one, his posts when explaining stuffs are always very good, I guess he does teach.Thanks IanB.

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: March 21, 2013, 01:18:54 am
content: This is an absolutely fascinating subject,well worth studying.Tesla understood it very well.http://books.google.com/books?id=XlMTAAAAYAAJ&dq=piano%20resonance&pg=PA49#v=onepage&q=piano%20resonance&f=false

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: March 21, 2013, 02:55:25 am
content: http://books.google.com/books?id=bhrreukJiLgC&dq=nikola%20tesla%20resonance&pg=PA348#v=onepage&q=nikola%20tesla%20resonance&f=falseAnd to stay on topic:http://en.wikipedia.org/wiki/Joule%27s_first_law

author: ve7xen
author_rank: Super Contributor
timestamp: March 21, 2013, 03:12:57 am
content: Quote from: IanB on March 20, 2013, 10:52:14 pmThis is very helpful, thank you.

author: ignator
author_rank: Regular Contributor
timestamp: March 21, 2013, 03:49:44 am
content: Quote from: c4757p on March 21, 2013, 01:01:50 amYou can describe this mathematically, but NO ONE has a clue what this is. I don't know why you would think any theoretical physicist does. You observe the effects, and can measure and design and make stuff, but we don't know physically what matter or any other physical things really are. They are still arguing about dark matter, dark energy, Higgs boson. Then there are some nuts at CERN that think they observed exceeding the speed of light. I want to know these people that understand this. We will someday, but that's not in the present.

author: c4757p
author_rank: Super Contributor
timestamp: March 21, 2013, 03:59:14 am
content: Quote from: ignator on March 21, 2013, 03:49:44 amI'm not going to address most of what you said - not to be dismissive, I just don't want to hijack the thread and start a philosophical argument. But I have to take issue with this. There aren't "nuts at CERN who think they observed exceeding the speed of light", there are scientists who had data showing that they exceeded the speed of light and were searching for an explanation. Most of them doubted that they really did exceed it, and IIRC they figured out what was wrong and had it down to an experimental mistake. It was the retarded pop-sci media that blew it up into "holy crap they broke the speed of light".

author: Rick Law
author_rank: Super Contributor
timestamp: March 21, 2013, 04:51:58 am
content: Speaking of sound, some energy will indeed be lost as sound. The humming you hear is mostly from transformers. The clicking you hear from relays, so on. Those are energy lost as kinetic energy transferred to wherever the sound may hit and vibrates whatever the sound hit.Electrons repel. When a large current is send through a wire, the wire will swell if however slight. Just like a garden host flexing when you turn on the water, turning on the current will flex the wire.Rick

author: Psi
author_rank: Super Contributor
timestamp: March 21, 2013, 05:10:52 am
content: Some energy will be turned to heat attempting to overcome friction and pull/repel all metal objects in the universe through magnetism

author: Rerouter
author_rank: Super Contributor
timestamp: March 21, 2013, 06:08:48 am
content: some energy is also lost in parallel conductors as they exert an attractive or repellant force on one another, like the above poster said, this is generally lost as heat on circuit boards, but on free hanging wires, depending on the current can physically move the conductors enough to be noticeable, and maintaining that force is what consumes the energy, providing acceleration opposing gravity,

author: AndyC_772
author_rank: Super Contributor
timestamp: March 21, 2013, 07:30:33 am
content: It doesn't require energy to maintain a force - only to exert a force and move it through distance.Work = force * distance, so power = force * velocity.

author: SeanB
author_rank: Super Contributor
timestamp: March 21, 2013, 08:28:51 am
content: Eventually all is lost as heat. The way it is converted to heat is the interesting thing. If it is directly converted, converted to light/radio before being absorbed, converted to vibration before being absorbed it is all converted to heat. No way around that in the universe, Entropy is always increasing.

author: Nirios
author_rank: Regular Contributor
timestamp: March 21, 2013, 02:56:45 pm
content: Quote from: IanB on March 20, 2013, 10:52:14 pmI know almost nothing about RF and that is one of the best analogies I've heard/read for antennas.So when does your online RF class start?? I'll be the first to signup.

author: ResR
author_rank: Regular Contributor
timestamp: March 21, 2013, 03:44:50 pm
content: I have an Ectaco Takser-E (Made in Estonia) used as a tabletop clock, 1995 era distance reader for power meters. It works fine, but it fills empty FM/AM/SW frequencies with constant noise of 50Hz modulated ~600Hz sound with 2Hz clipping. So sometimes energy is lost as RF energy.http://sphotos-e.ak.fbcdn.net/hphotos-ak-prn1/45023_406002672812512_718706042_n.jpgI connected Schurter 5110.1033.1 with X-rated 0,1uF 275VAC capacitor soldered to output of the filter to mains cable as close to the device as possible and it didn't had any effect so the device itself transmits the RF energy.(Also it gets warm and heats up anything that is placed on it to 30...35°C)

author: 4to20Milliamps
author_rank: Regular Contributor
timestamp: March 22, 2013, 10:36:07 am
content: More stuff to ponder:Attenuation and absorptionhttp://en.wikipedia.org/wiki/Attenuationhttp://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)

author: CarlG
author_rank: Regular Contributor
timestamp: March 23, 2013, 04:11:04 pm
content: Sorry, really of topic, but...Quote from: ignator on March 21, 2013, 03:49:44 amThere's nothing strange about exceeding the speed of light. E.g. there is Cherenkov radiation, which is emitted when a particle moves in a medium at a speed faster than the speed of lightin that medium. Well known in particle physics, Cherenkov radiation is used as part of event detection mechanisms.Also, if I remember correctly, in RF transmission lines, you can have a (reactive) wave front propagating faster than the speed of light (in vacuum), created ar the intersection of two superimposed waves. I'm no expert in RF so I may have got it wrong, but that's basically how it was explained in some class att the university.It's only the speed of lightin vacuumthat is a definite barrier for an object with a mass;)

author: nukie
author_rank: Frequent Contributor
timestamp: March 24, 2013, 06:30:39 am
content: Is sound a product if rf energy? Humming is also power lost.

author: ignator
author_rank: Regular Contributor
timestamp: March 25, 2013, 01:06:23 am
content: Quote from: CarlG on March 23, 2013, 04:11:04 pmTo quote wikipedia "Cherenkov radiation results when a charged particle, most commonly an electron, travels through a dielectric (electrically polarizable) medium with a speed greater than that at which light would otherwise propagate in the same medium".Cherenkov radiation does not exceed the speed of light, it occurs when an electron (in this case) traveling in a medium (in this case water), and the electron exceeds the phase velocity of light in the medium, the phase velocity is comparing their two speeds, light in water is .75c (1.33 is index of refraction for water, the recipical is the relative speed decrease of the light in water), and the electrons are moving typically at .95c, this radiation is energy caused by the electrons motion through the medium. As the electron is loosing energy, it's velocity is decreasing (this keeps this germane to this thread), and this light absorbed is energy, and results in heat.