I guess this is getting a bit off-topic for DIY.
Hey, ever heard of SEAgel, the inexpensive aerogel material?
http://www.youtube.com/watch?v=HoCAxS4vqwQ
I expect that sound waves should travel very slowly inside seagel. I wonder if it can do anything interesting. Stuff your bass drivers full of low-velocity aerogel magic?
Also, has anyone here tried building Woody Norris's "Hypersound" or HSS sonic flashlight devices? A low-fi telephone quality version should be fairly simple. Here's a Japanese website with a hobby project:
parametric speaker
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I've been interested in that aerogel material for some time, but I don't know if it's easy to get yet. There would seem to be all sorts of applications- a lightweight stuffing for tonearms for example.
I collect scientific and engineering books, mostly prior to the 1970s. It's my view that earlier books were labors of love by college professors who were focused on teaching, and were writing something for people headed for practical engineering careers. Think Timbie & Bush, Stout's book on measurements, Corcorran on AC, transients and circuit analysis and of course almost anything written by Terman. Later books tend to be abstract mathematical nightmares that illuminate very little. The difference is really striking if you compare an early optics textbook with a current one. Who knows how correct they are? OTOH, it's a far more mathematical world we design in, so people who don't have that leaning are probably dinosaurs with little future.
I collect scientific and engineering books, mostly prior to the 1970s. It's my view that earlier books were labors of love by college professors who were focused on teaching, and were writing something for people headed for practical engineering careers. Think Timbie & Bush, Stout's book on measurements, Corcorran on AC, transients and circuit analysis and of course almost anything written by Terman. Later books tend to be abstract mathematical nightmares that illuminate very little. The difference is really striking if you compare an early optics textbook with a current one. Who knows how correct they are? OTOH, it's a far more mathematical world we design in, so people who don't have that leaning are probably dinosaurs with little future.
Well, actually I'm describing how my talks about electricity usually go.
Example: First I point out the existence of contradictory definitions of the word Electricity. Then I use the proper scientific definition of quantity of electricity, where electric current is a "flow of electricity." Then I point out that electricity in a flashlight flows in a complete circle, going through the battery and through the bulb. It circulates over and over with none being gained or lost. I point out that electricity therefore cannot be a form of energy ...and if any book is states that electricity is a form of energy, that book is wrong.
Then someone from the audience usually says "Well, after all, electricity is really just a kind of event."
Then I say "that doesn't help the situation. The existing problem involves multiple contradictory definitions. You're adding yet another definition when there are already too many."
It's not straw man. Instead it's what actually happens over and over during my lectures in the real world. Therefore, in order to keep my readers from pulling that ploy too, I head them off by describing it in my articles. Hopefully I give my counterargument before they've even thought of it themselves.
Because of this typical audience behavior, it appears to me that people want to deny that any problem exists; want to try re-defining the word Electricity yet another time in order to duck the issue. I block that easy escape.
For interesting background on this psychology, see:
The Science of Why We Don't Believe Science
The Science of Why We Don't Believe Science | Mother Jones
This has been extensively tried by many others for many decades. Have you heard the big bruhaha about textbook errors? I doubt it. Everybody else tries to be polite and properly academic, and in response they get ignored. Me, I use my website to make a big stink, and as a result I get the problem publicized in the Boston Globe. Then at long last others pick up the trail too. (Once it's been in the Boston Globe, suddenly it's legit!)
TEXTBOOKS FLUNK OUT, May 1999 Boston Globe
virus: virus: Fwd: Textbooks flunk out
GREAT AMERICAN TEXTBOOK SCANDAL Forbes 2000
Forbes.com - Magazine Article
IN THE BAD BOOKS, Beyond 2000 (archive.org)
Beyond 2000 | Science-General | In The Bad Books
As a direct result of this and other provocative accusatory articles, the state of Texas instituted a policy where school textbook publishers would receive a huge fine for each textbook error found. Texas determines the contents of textbooks nationwide, since Texas is the biggest customer of the K-12 publishers. But all that stuff is extremely political, and I think the policy was quietly struck down before any grade-school publishers received any actual punishment.
Again, please point out the URL and paragraph where this happens. I can't fix it if I don't know where it is.
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Hmmm... maybe that's why I almost never use the word electricity. It doesn't have any clear definition in my mind the way current, voltage or electromagnetic spectrum do. It doesn't explain or quantify anything. Actually it works best in the form, "There was a lot of electricity in the air on opening night."
The fact that 'electricity' is not gained or lost is perfectly consistent with it being a form of energy, in fact if it were energy such conservation would be exactly what you should expect. In both cases you have a conservation law, but it just happens to be two different laws.wbeaty said:
I think the problem is that 'electricity' is a general layman's term for a whole class of EM phenomena. When first introducing a subject it can be quite difficult, and even counterproductive, to avoid saying things which later need to be corrected. If you insist on avoiding this then the result will often be confusion, as people are asked to get details right before they have grasped the big picture.
I will give a mathematical example. When people are first taught about the concept of 'function' they are almost always told that a function produces a value from one or more inputs. The idea of a multi-valued function would just confuse them, so it is never mentioned. Later, they may need to be told that their original idea was not quite correct as multi-valued functions exist. This may be poor logic, but it is excellent teaching. I guess you would say that the elementary maths teacher must teach the correct definition of 'function' (i.e. a possibly multi-valued mapping from a domain to a range) to children who are still struggling with basic algebra. This is good logic, but poor teaching.
Um. What? Better check any physics book aimed at high school or above.
Electricity flows through a battery with none being gained or lost. Exactly as much flows in as flows out. One coulomb per second inwards, one C/sec outwards. None is used up, none is created. Yet the battery is being drained, and soon it's dead. Confusion! How can we justify the vanishing energy?
Electricity flows through the light bulb. The same amount goes in as goes out. No electricity is lost as it passes through. Yet significant wattage of light/heat appears?!! Something is screwy. Perhaps coulombs are different than joules. Perhaps the coulombs of electricity are not a quantity of energy.
So an electric current isn't a flow of electricity? Are you rejecting my explanation, and instead saying that electricity is really just a kind of event?
No, the actual problem is that electricity is not a form of energy, yet most books say differently. They are wrong.
Here's the usual scientific definition of electricity:
CRC Handbook, 64th Ed
Quantity of electricity or charge -- The electrostatic unit of charge, the quantity which when concentrated at a point and placed at a unit distance from an equal and similarly concentrated quantity, is repelled with unit force...
Coulomb (unit quantity of electricity) -- the quantity of electricity transported in 1 sec by a current of 1 A. A unit quantity of electricity. It is the quantity of electricity which must pass through a circuit to deposit 0.0011180g of silver from a solution of silver nitrate. An ampere is 1 coulomb/sec. A coulomb is also the quantity of electricity on the positive plate of a condenser of one-farad capacity when the electromotive force is 1 v.
Electric charge (Q) -- The quantity of electricity; i.e., the property that controls interactions between bodies through electrical forces.
Quantity of electricity or charge -- The electrostatic unit of charge, the quantity which when concentrated at a point and placed at a unit distance from an equal and similarly concentrated quantity, is repelled with unit force...
Coulomb (unit quantity of electricity) -- the quantity of electricity transported in 1 sec by a current of 1 A. A unit quantity of electricity. It is the quantity of electricity which must pass through a circuit to deposit 0.0011180g of silver from a solution of silver nitrate. An ampere is 1 coulomb/sec. A coulomb is also the quantity of electricity on the positive plate of a condenser of one-farad capacity when the electromotive force is 1 v.
Electric charge (Q) -- The quantity of electricity; i.e., the property that controls interactions between bodies through electrical forces.
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Drained of what?
"Quantity of electricity or charge", 'Coulomb (unit quantity of electricity)", and "Electric charge (Q) -- The quantity of electricity". Quantification is not the same as definition.
FWIW, my electronics dictionary* defines electricity as "Phenomenon of positively and negatively charged particles of matter at rest and in motion, individually as well as in great numbers."
I suppose saying electricity is energy is akin to saying a log is a campfire. It's really just potential.
*Douglas-Young, John, Illustrated Encyclopedic Dictionary of Electronics (Parker, 1981)
I have read many physics books aimed at levels considerably above high school, so any errors on my part are certainly not due to lack of 'checking'.wbeaty said:
I am not confused. The chemical energy from the battery mostly ends up as heat energy. Most energy ends up as heat, as thermodynamics tells us. No energy vanishes.
An electric current is a flow of electrons (or, sometimes, holes). I am neither accepting or rejecting your 'explanation'. I am not considering your 'explanation'. I was merely pointing out the flaw in your statement that as 'electricity' is conserved it cannot be a form of energy - on the contrary, being conserved would be a requirement if it were a form of energy. There is certainly such a thing as electrical energy, so the books are not completely wrong when they introduce electricity as a form of energy. They are just trying to be helpful. There ought to be separate books written for pedants, but I am not sure how easy it would be to define electricity when you can't talk just about electrons but also holes, muons, pions and all the other things with electric charge (and Noethe's theorem and magnetic monopoles and discrete quantum numbers and spontaneous symmetry breaking - all this before you can talk about light bulbs).
I think your confusion arises from your insistence that electricity 'is' something. Much better to use the term 'electricity' in a general sense for a whole range of EM and related phenomena. Then you can go on to tell people that 'electricity' includes the concept of electric current (a flow of electric charge), electrical energy, EM waves etc. etc. Your nitpicking is an excellent illustration of the difference between knowledge and wisdom.
What do light bulbs need in order to produce light? What do batteries lose as they go dead? What do you buy from electric companies?
In physics, defining a quantity is everything. What does "volume" mean? What does "length" mean? The above references are defining "electricity" as meaning the same as "charge." What is electricity? Physics says that it's coulombs, not joules or volts. That's the scientific definition of the word "electricity."
Yep, that's one of the usual non-scientific definitions. Here's Merriam-Webster...
A fundamental form of energy observable in positive and negative forms that occurs naturally (as in lightning) or is produced (as in a generator) and that is expressed in terms of the movement and interaction of electrons
Electricity - Definition and More from the Free Merriam-Webster Dictionary
So Merriam-Webster thinks that batteries produce Positive and Negative Energy? Really? Physicists long ago postulated the existence of "Negative Energy," and recently astronomers have probably discovered it as the cause of accelerated expanding universe, ...yet here it was inside your D-cells all the time! Stupid scientists! (Actually no. The Merriam-Webster definition is simply wrong. And MW dictionary did once have the correct definition about 20 yrs ago, but someone changed it into the garbage above. Positive and negative energy, sheesh.)Electricity - Definition and More from the Free Merriam-Webster Dictionary
You could also say that length is measured in kilograms, or that time is measured in cubic inches. But those aren't scientific definitions.
Saying that electricity is the volts (is the potential) is adding ANOTHER definition to the unscientific morass.
OK, which of the below is the correct defintion (the one defined by physics?)
- Volts of electricity
- kilowatt-hours of electricity
- watts of electricity
- amperes of electricity
- coulombs of electricity
- "electricity" is like "biology" or "optics," it's really a phenomena-class
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I think you've put your finger on it. "Electricity" is a general and colloquial term. It is not a precise scientific term like "flow of electrons." It can mean "energy generated remotely," as in, "Wow, look at the bill for electricity we just got!" It can mean "flow of electrons." It can mean "flow of ions through a solution." It can mean "flow of solitons." And so on and so on.
Your questions on specific aspects of electricity can best be individually answered by more precise terms instead of the general. And the general term encompasses more phenomena than just your particular set of questions. The answer to your definition question is, "all of the above."
Your questions on specific aspects of electricity can best be individually answered by more precise terms instead of the general. And the general term encompasses more phenomena than just your particular set of questions. The answer to your definition question is, "all of the above."
Electrons dont realy flow (in wires) as such, more stagger around slowly from one atom to the next
As regards to electricity, there is the circuit view, electrons flowing! around the wires and the physics view, TEM waves, both are relevant in the world of electronics, as are the other descriptions, it depends on how you are looking at a circuit, a product or a design.
As regards to electricity, there is the circuit view, electrons flowing! around the wires and the physics view, TEM waves, both are relevant in the world of electronics, as are the other descriptions, it depends on how you are looking at a circuit, a product or a design.
But your following statement shows that you really don't know the difference between coulombs and joules:
Physics textbooks never say that coulombs and joules measure the same thing. If electricity is never gained or lost during its passage through an LED, how can the LED convert any electricity into optical energy? If electricity was energy, then we'd have 20mA flowing into an LED, and 15mA flowing back out (with 5mA turned into light.) But the LED sends every bit of electricity back out through its second lead. Not one bit gets converted into light. It's because electricity isn't a form of energy.
Put simply: in circuits the electricity flows in a complete circle, going around and around repeatedly without gain or loss. But at the same time we have energy sources (e.g. battery) and energy sinks (e.g. resistor.) How to solve this confusion? Again very simple: there are two separate things flowing in circuits. Electricity is measured in coulombs, and electrical energy is measured in joules. Two things, and it's very confusing if we label them both as "the electricity." Instead the flow of electricity is measured in coulombs/sec or amperes, and the flow of electrical energy is measured in joules/sec or watts. The flow of electricity is not measured in watts. LEDs absorb/remove milliwatts of electrical energy, not milliamperes of flowing electricity.
How can it ever escape from the battery if it all must flow back in again? If input exactly equals output, then there is no net output. To cut through the confusion, simply accept that electricity is not a form of energy. Electricity flows through the battery, and at the same time the battery is putting out electrical energy.
It's not "my" explanation. It's the one that's in all the physics texts.
Um. Where did I say that? I said that electricity flows in a complete circle. How can electricity be a form of energy if no electricity ever leaves the battery? (If it flows through the battery, with inflow exactly equalling outflow, then the battery doesn't supply any electricity. It just pumps it.) It's not that complicated: physics texts show us that coulombs are not joules. A little thought shows that the books are right: a battery sends out joules of energy into the circuit, but at the same time the colombs of electricity flow through the battery without gain or loss. Two different things are flowing. The big confusion occurs when we define electricity as coulombs, and also say that electricity is a form of energy, that electricity is joules. (It's very much like thinking that sound and wind are the same thing. They're both invisible, right? And a big bass speaker emits wind and sound, so they must be the same. Ah, but the wind goes back and forth, while the sound waves move continuously forward. And in AC circuits, the coulombs wiggle back and forth over a tiny distance in the wires, while the joules move forward across the entire wide circuit.)
No, they're completely wrong. Physics texts define electricity as the coulombs. If some K12 text instead teaches that electricity is really the joules, then that book is wrong. And if a book said that length is measured in gallons, it would be wrong in basically the same way. What if hundreds of K12 books said that length is measured in gallons? Doesn't matter. Science is not determined by voting. All those books would be wrong.
All science textbooks MUST MUST MUST be written by pedants, or in other words written by content experts who know to avoid sowing confusion by using incorrect definitions of the terms they use. Otherwise you'd get a morass of mistakes and misled students. (Imagine grammar textbooks written by grammar non-experts and filled with incorrect usage. Imagine using such a book to teach english to non-native speakers.) The problem is much worse for science textbooks. Where electrical science is concerned, we're all non-native speakers. And we all learned electricity from books written by non-nitpickers and full of wrong ideas. Engineers know how to fix this. Just give up on ever understanding electricity in any visual/intuitive way, and instead concentrate on the math. The engineering equations are correct, and they cut right through the impenetrable confusion caused by K12 textbook errors. But if we only have SPICE programs, and no sensible verbal descriptions, then somehow we're missing something.
On the other hand, out here in the everyday world we can use words in any way that gets the message across. But inside textbooks, the experts have to agree upon the clear narrow definitions of words. You can't have one book saying that time is measured in seconds, and another book teaching everyone that time is measured in gallons. Do that and everyone would be totally confused about the word "time."
Physics textbooks state that electricity 'is' the electric charge. Electricity is the coulombs, and a flow of electricity is measured in terms of amperes. Your confusion about joules and coulombs arises from thinking that the NIST isn't correct. If you seriously believe that the NIST is wrong in stating that electricity is measured in coulombs, and you want electricity to also be measured in joules, then you're dangerously close to becoming a crackpot. Joules and coulombs are as different as meters and seconds. Should time be measured in gallons? We can check the NIST website and find that that's wrong: time comes in seconds. Should electricity be measured in joules? Check the NIST website and see that it's measured in coulombs. Joules is wrong, and it doesn't matter how many K-12 textbooks disagree. The NIST has the final say, and books which say differently are teaching confusion because they're using non-standard definitions which contradict standard physics.
That's actually fine, because then "electricity" is something like "weather" or "physics." But still it opens the way for crazy statements: If you catch some rain, do you have a bucket of weather? Is rainwater made of weather, but river water is not? Is a spinning flywheel full of physics? And when it stops spinning, the physics is all gone? (This is an analogy for capacitors: if electricity is a phenomena-class like "physics," then you can't ever put electricity into a capacitor. It would be like charging up a flywheel with "physics.")
If I insist that textbooks must employ proper usage of physics terms, and you redefine this as "nitpicking," that's a good example of using a rhetorical ploy during a scientific argument: good for fooling people and swaying audiences. But as Feynman pointed out, scientists must carefully avoid such stuff, since Nature cannot be fooled.
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Of course electricity is a precise scientific term. That's why it appears in the CRC handbook and on the NIST website of physics standards. In physics/engineering, a flow of "electricity" is called "electric current." Flows of electricity are measured in amperes, and a quantity of electricity is measured in coulombs. And if you use any colloquial definitions of "electricity" in a physics textbook, that's called "being wrong."
Similar situation: "power" is a general and colloquial term which usually means energy. But also in physics and engineering, "power" is employed in a very narrow sense: it's the joules per second. As a result, some physics students become confused. They don't realize that "power" in physics has a different meaning than the one they grew up with. (E.g. do Power companies sell power? Sure. That's colloquial usage of the word. But a physicist would say that this is wrong, since in fact energy companies sell energy, and you pay by the KWH and not by the watt.)
And as before, if a physics textbook author starts including the colloquial meaning where "power" really means energy, that textbook can confuse the students ...because it's wrong.)
Which is the correct definition of the word "power?"
1. energy
2. energy flow or energy transfer
Number two is correct. Number one is the incorrect non-scientific colloquial definition.2. energy flow or energy transfer
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Electrons dont realy flow (in wires) as such, more stagger around slowly from one atom to the next
Nah, it's just like with wind: air molecules vibrate around at incredible speed all the time. But during the wind, they also have a net forward motion. In all metals the electrons are constantly whizzing around. But during an electric current in a wire, the electrons also have a net flowing motion.
Here' an excellent website which shows the flowing charge inside conductors:
Nope, both are the physics view. There are amperes, or the coulombs of flowing electrons. There are also the watts, or the joules of flowing electromagnetic energy. In AC circuits the coulombs wiggle slightly back and forth while the joules flow rapidly along at almost the speed of light. Here's a comparison of the two:
Come on, what is electricity REALLY? Electric charge flow versus EM energy flow
SCIENCE HOBBYIST: Electricity F.A.Q. ANSWERS
SCIENCE HOBBYIST: Electricity F.A.Q. ANSWERS
I have to ask, but how does electricity flow into and out of the second lead, would not this be a more correct definition of the flow of electricity:
Printed Circuit Design & Fab Magazine Online
So it flows from the source, ie battery to the load, eg light bulb, it dose not realy flow round the circuit as a line of happy whizzing electrons (that only average 84cm per hour) round the wires, so the energy is converted to heat, light etc.
Printed Circuit Design & Fab Magazine Online
So it flows from the source, ie battery to the load, eg light bulb, it dose not realy flow round the circuit as a line of happy whizzing electrons (that only average 84cm per hour) round the wires, so the energy is converted to heat, light etc.
Some interesting views on this site. I am also currently reading his book "the fields of electronics".
Welcome
Again though electrons dont realy flow in wires, they meander at approx 84cm per hour, and dont usually travel that far, cos they are lazy. The waves travel at some speed below the speed of light, approx 0.6X roughly, depending on the dielectric sourounding the waveguides (wires, PCB traces etc).
Welcome
Again though electrons dont realy flow in wires, they meander at approx 84cm per hour, and dont usually travel that far, cos they are lazy. The waves travel at some speed below the speed of light, approx 0.6X roughly, depending on the dielectric sourounding the waveguides (wires, PCB traces etc).
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