studiot

I said no such thing. Here is a quote from a GCSE (junior high school) revision site. Note they divide the part of the atmosphere you refer to into four layers. Stratification is still a rose by any other name. Note also that although they don't large discuss variation of composition with altitude their diagram clearly indicates that it varies since they show a water ceiling and a natural ozone layer. The atmosphere Layers in the atmosphere The atmosphere is the layer of gas around the Earth. The atmosphere can be divided into four parts: Troposphere: Where we live. Stratosphere: Some jet aircraft. Mesosphere: Space shuttle orbits within. Ionosphere: Mainly charged particles.

Quick reply, I will return again after I have digested your additions. Yes Fourier and his law of heat transfer is one two names I had in mind. Newton's law of cooling was the other. Standard heat transfer calculations are based on these. However you need to be careful if this is a building calculation because there are standardised approximations and assumptions made for the simplification of the calcs so they do not have to be worked from first principles every time. For building control purposes these standardised methos superceed first principle calcs. You mentioned the complexity of some maths you have found. Solutions to the equations have two aspects. Steady state and transient. The transient solutions are much more complicated and these may be what you have found. However Fourier's law does admit trigonometric series solutions for both cases. Edit add the following material Here is a good discussion of the maths. https://www.thermalfluidscentral.org/encyclopedia/index.php/One-dimensional_transient_heat_conduction_in_semi-infinite_body The first part of the article gives the basic time independent equations. The part you will be interested in starts at equation 23 where a periodic heating function, as you seem to indicate, is introduced. The analystical solution is then presented followed by a neumerical solution from equation 44 on. Note that in the numerical soltion an approximating function is used (they used a cubic, equation 50).

Sorry Fred, but you just mentioned the atmosphere, which does have layers as I described. JC refers only to the lower atmosphere which has such an overwhelming concentration of oxygen and nitrogen that any variation of other gasses (eg carbon dioxide is about 0.03 %) tends to get lost in the big figures. The other layers form the upper atmosphere and carbon dioxide does not extend this far so its presence largely concentrated in the lower atmosphere band.

OK so You disagree with this national document (in declaring my points irrelevent). http://www.nhbc.co.uk/NHBCPublications/LiteratureLibrary/Technical/filedownload,29440,en.pdf which says that carbon dioxide pools in depressions and methane collects under soffits, ceilings and other spaces confined by horizontal building elements. The document has extensive bibliography at the end to national research and controlling documents. There is also lots of other useful info about the gases. I wish I had this when participating in the design and construction of the Priory Fields commercial and the Salmon Parade residential developments in the 1980s. You are entitled to your opinion and I am entitled to mine without vitriol.

Hello Thomson and welcome. Please note that homework/coursework belongs in the homework section. It is also wise to allow sufficient time to gather responses on a science website, one day is not enough. Finally you need to post the actual question (don't worry about the greek letters we can help with that plus some idea of your thoughts about the question. Yes you need to derive a differential equation with respect to time for the heat flux. What physical laws or theorems do you know in relation to heat transfer? Hint they are associated with names of two of the giants of applied maths.

Strange, I have added +1 since I take it in good spirit, not as in any way disrespectful for those three souls who died in that hole (which I think was in Kent by the way)

Since I have no intention of turning this into an unseemly schoolyard slanging match I am going to make brief comments of the last couple of posts then present my own alternative view, which does not accord. Fred can then choose his own. interpretation. Thank you , John for all that working off of the Sunday roast. I don't doubt you figures except for one thing. You clearly misunderstood my example about the hole in the ground. I said, and I meant, that the Earth's atmosphere ie stratified. And that that statification is due to the varying pull of gravity on molecules of diffeent molecular weight. I should have added there is a second mechanism at work so will detail this in a moment. Stratified not continuously graded. Stratified means 'divided into (horizontal) layers of different composition. I am taking the atmosphere as being that body of gas that has a gravitational attachment to the Earth. So my information is that the layers are as follows. Up to 72 miles the composition is basically a mix of nitrogen molecules and oxygen molecules with 'traces' of other gasses. Since the molecular weight of nitrogen and oxygen is almost the same, and as John says, the molecules are moving pretty fast, there is no further stratification and negligable gradation within this layer. The composition changes above this height as the oxygen molecules and to a lesser extent the nitrogen dissociate. At about 600 miles the composition changes again the principle gas now being helium At about 1500 miles the composition changes again and this is where you will find most of the hydrogen in the atmosphere. Gasses beyond 21,000 miles have an average speed in excess of escape velocity so that is my upper limit of the atmosphere. So my stratifiaction occupies 5 distinct layers for the whole atmosphere. Now note layer 5 in particular. Mostly hydrogen. To bring this back to the Earth's surface and what I said about 'lighter' molecules consider the following thougth experiment. Line up some moderately tall jars of gas with lids. The jars contain carbon dioxide, nitrogen, methane, hydrogen. What will happen when I remove the lids? Why do you think gas detectors in buildings are mounted on the ceiling not the floor? I think the hydrogen leaves the jars immediately and heads skywards. The methane also migrates quickly upwards (hence my question about gas detectors). The nitrogen jar will take perhaps one hour to exhange enough molecules to have the same nitrogen/oxygen ration as the surrounding air The carbon dioxide will remain in the jar and still be in greater concentration than normal on the following day.

How does that address my post 34?

The multidimensional equivalent of the derivative is called the Jacobian and usually appears in Matrix form. https://en.wikipedia.org/wiki/Jacobian_matrix_and_determinant

This is difficult to answer since I don't know where you are, what your interest in electronic/electric circuits or what you have access to. Most of the books I would recommend are British, simply because most of my library is from British publishers, though I have some good American ones as well. First to distinguish between electric circuits and electronic circuits. The main applications of electricity are power (which includes domestic drills, heaters etc) and information/communications. Electric circuits are more geared towards power engineering and most books with this title may or may not have a chapter or two on electronics. Conversely Electronic circuits tell you about , well electronic circuits, have scanty basic information about power applications. Both are intensely practical subjects so the next question is what do you want this for? If you are following a recognised course towards professional application then you will need much more theoretical detail. If this is an amateur interest then a more practical approach that offers the right amount of the right theory would suffice better. For an amateur and even professional introduction to electronics with a wide ranging coverage the books by Michel Tooley and his Brother are brillaint. They offer a great deal of the type of 'why are we doing this' explanation I put into my posts above. 'Electronic Circuits' was one of the originals but there have been several new ones and revisions. http://www.amazon.co.uk/Electronic-Circuits-Fundamentals-Applications/dp/0750669233 Two other good books in the professional + amateur category are A Practical Introduction to Electronic Circuits Martin Hartley Jones Electronics and Electronics Systems George H Olsen Before you pay for the oft recommended american 'The Art of Electronics' by Horowitz Get it from the library and check it out. I cannot recommend it. A brilliant american book is Microprocessors and digital systems Douglas V Hall A good modern electrical circuits first serious book is Electrical Circuit Analysis and Design Noel M Morris Finally try this site, they were a really good bunch before they were taken over by a commercial enterprise, so beware the advertising, but they have the internet rights to the famous e-textbook by Tony Kuphaldt. allaboutcircuits.com Also beware the original Kuphaldt book uses the 1990 fashion of electron flow as the positive direction for current flow which can cause confusion. This is not a good idea and but was fashionable in the 1990s. In fact always check the work of any author anywhere before reading as to whether he uses what is known as conventional current (postive in the direction positive to negative) or electron current (positive in the negative to positive direction) Post again if you need more.

Two responders here have chosen to limit the atmosphere quite arbitrarily. Fred did not do that in his OP. We have also had a recent thread about the 'limit' of the atmosphere and these arbitrary limits were discussed, but the physics answer was that the atmosphere never actually stops in our models. Yes there are good reasons for these limits but that was not the question. I still challenge that. Consider a shaft in the ground 2 metres square in section, 5 metres deep and open to the atmosphere. However the the atmosphere in the shaft comprises over 20% carbon dioxide. How long will it take for the atmosphere to equalise with the lower % in the normal atmosphere above? In case you are wondering this was the standard video shown in 1990 by HSE when I did my confined space training. Three men died of suffocation in that shaft over the course of more than a day.

Does it? Then why does it list the composition of the atmosphere at 1000km altitude?

Is that so. Then perhaps you can explain away these figures. http://wordpress.mrreid.org/2014/08/01/the-composition-of-earths-atmosphere-with-elevation/

Neither. In the abscence of a body force a gas expands to fill its material container. The atmosphere has no material container, except at the surface of the Earth. So it is contrained to Earth by the body force of gravity. Now gravity acts differentially on 'heavier' (more massive) particles. We can see this effect in the settling of suspended particles in a liquid. The heavier particles settle first at the bottom and we and up with the lightest on top. The average molecuklar weight of atmospheric particles (molecules) is 30 but carbon dioxide the mw is 44 so you can see it is a 'heavier' particle. The the gaseous makeup of the atmosphere is stratified, like the settling sediment in water with the greatest concentration of carbon dioxide at the Earth;s surface and the percentage of lighter gases increasing with altitude. The stratification is not banded it is gradual. That deals with vertical distribution. Horizontal distribution is fairly even since the mixing times for a gasesous atmosphere is measured in days. By contrast the ocean mixing times can be measured in years to centuries. In the atmosphere, just as in the ocean, where you get a continued concentrated input there will be local variations and a balance will be set up between input and dispersal.

Welcome, bay, and thank you for your contribution. Don't you think you are unecessarily and arbitrarily limiting the definition of nothing to the abscence of concrete nopuns? What about all the abstract nouns like love, hate, tiredness, celerity, and so on?

No. In fact if you had asked the question does an electric generator need magnets at all the answer would still be no. A simple example is piezoelectric generators. There was even a proposal and some experiments to recover energy from vehicles braking by the use of 'hit plates', using this method.

Now that we have the beginning's of a circuit, I can comment on Stranges post#17 and your over-casual dismissal of it. In a perfect world Strange's comment would be correct. You have gained nothing in power efficienty terms over a straightforward DC supply at the same voltage. However in the real world your configuration has reduced power efficiency significantly since all real world supplies have an internal impedence. The internal impedence of the 'off' supply would appear as a load in parallel to the load resistor for the 'on' supply. In other words the on supply would try to drive current back through the off supply. In addition to ineficiency, this is likely to lead to the early demise of one or both supplies. I forget which but it is rule 0 or rule zero that you do not connect two outputs together without very special measures.

Connecting them both to what? That is why I keep asking for a full circuit digram.

I don't quite get what you actually 'know about' after repeating my post 3 times, But I respectfully suggest your second sentence indicates you need to know more about electrical power theory and practice before making judgements.

If you are not sure why do you think it is very stupid, or even a little bit stupid.? We can discuss it if you wish, I am not trying to hide details. Why are you avoiding my question about distribution details? Whatever the waveshape,AC or DC it is the RMS current that is important to determine the power. Since we buy and use electricity in terms of power not current a given supply requires a specific RMS current and therefore the wires have to be the same.

Please don't anyone try these experiments. Old time service engineers were taught to keep one hand in their pocket when probing around electronic circuits in case they accidentally touched a live (at DC) terminal. I can tell you that even the bite from the 90volt battery they used to use in valve portable radios hurts and has been known to kill. Directdude, electricity is dangerous. But properly treated it is also useful to essential so let us concentrate on your 3 wire distribution system. You need to provide proper details to discuss, it is up to you, not me, to work it out for you. I note that 3 wires is one more wire than 2, which represents a greater than 50% cost increase since it would also require stronger support structures. I can't comment more without knowing what the proposed voltages at all stages are. Please also note that most consumers receive their current AC supply over 2 wires. In the US this is transformed to what is correctly known as split phase, although too many call it two phasse, which it is not. There were once DC supplies in both the US and Europe, which were abandoned for very sound technical reasons. There have been experiments in the US with superconducting primary distribution extra high voltage lines at DC. But at the consumer end, the size, weight, cost and efficiency of machinery and some circuitry is least at DC and rises with increasing frequency at AC. Why do you think most vehicles now have alternators rather than dynamos?

From John Donne 'Undertaking'

This statement needs amplification. Further I cannot agree with you about safety. One characteristic of DC is that a victim who has grasped a live conductor cannot let go. This is not true at AC.

I thought this question was going to be more difficult than it turned out. To understand the voltage distribution use the simplest model for a transistor. This is a pair of 'back to back' diodes as shown in my sketch (correct for an NPN 2n3904 transistor). This means that the pair block in both directions between collector and emitter when nothing is connected to the base. So any current flowing will be the collector - emitter leakage with abse open circuit Iceo Now look first at the BE diode. It is forward biased, that is it allows current to flow in the direction from the +9 volts to 0 volts. An ideal diode has zero forward resistance so both terminals will be at the same voltage. The actual diode will be very close to this so the emitter is set at zero so the base will be slightly more positve as observed. Now look at the CB diode This is reverse biased so blocks current. The collector is set at +9 volts. This is the cathode of the upper diode If this were an isolated diode you could tie the anode of this diode to any voltage and it would be blocked. In this case the anode is also the base of the transistor which is set to near zero by the forward biased lower diode. As regards to the electric field part of the question. The electric field and potential in a resistor change (perhaps linearly) along the resistor from one end to the other. Components acting like this are said to be acting in resistive mode. The field and potential change abruptly across a reverse biased diode whose action is blocking. This is like a capacitor and components acting like this are said to act capacitively or in capacitive mode. It may be of interest to know that this ability of a reverse biased diode to act capacitively is exploited in so called varicaps or voltage dependent capacitors.