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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.
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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.
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I wish it was lost as muffins...
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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?
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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?
RF 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. -
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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.
I 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? -
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.
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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?
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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.
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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.
I 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. -
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?
A 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. -
A 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).
This is a pretty good analogy. -
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.
Careful with "they". You'd be surprised how well some of this is understood by many people. -
A 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).
Great big
to you. That's a good one. Do you teach?
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Great big
+1, great one, his posts when explaining stuffs are always very good, I guess he does teach. to you. That's a good one. Do you teach?
Thanks IanB.
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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 -
A 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).
This is very helpful, thank you. -
You 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.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.
Careful with "they". You'd be surprised how well some of this is understood by many people. -
Then there are some nuts at CERN that think they observed exceeding the speed of light.
I'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". -
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
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Some energy will be turned to heat attempting to overcome friction and pull/repel all metal objects in the universe through magnetism
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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,
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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. -
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.