studiot

Hi Ed, yes there are several viewpoints and I know that many (including Wiki) use the term pulse frequency without much thought. The problem is Consider a pulse, 10 nanoseconds long, repeated every 10 microseconds. What are you using to define the frequency the 10 nanoseconds or the 10 microseconds? Do you think a circuit with a bandwidth of 100khz would pass this pulse train? The term frequency can be used with some meaning for a square wave and you could expect a square wave with an 'on' time of 5 microseconds and an off time of 5 microseconds to pass such a circuit with some rounding but a still appearing as a recognisable square wave. Very short pulses need additional information to describe them properly, which is why radar engineers invented PRF and all the other terms. Your interposing cloud of electrons would appear to me to constitute a plane rather than a pulse?

The math huh http://mathworld.wolfram.com/DeltaFunction.html There are some pretty pictures of a sine expansion, amongst others. But see also my response to Strange below. I particularly liked your last sentence, emboldened, especially the bit about pulsed DC, which is what I was talking about and Handy would be generating. What exactly is the non zero portion of a perfect pulse if not DC? It is a stright line parallel to the horizontal axis. Because of this when designing say pulse transformers or transmission lines etc it is common to break the puls into three sections. Section 1 The rising front is analysed by high frequency equations since it has many high frequency components, Section2 The flat top is analysed by DC or low frequency analysis since it ideally has zero freqency components Section 3 The trailing edge is analysed by HF analysis as the leading edge. An additional pulse characteristic called droop is introduced in real world analysis of section 2. This sort of situation appears in radar systems, and in analog power supplies where enormous current pulses occur for very short durations during the reservoir charging/discharge cycle. See here particularly the quote underlined. http://www.thefouriertransform.com/pairs/impulse.php Frequency = 1/wavelength yes? So what is the frequency of a zero length pulse? So I am saying that both terms are inappropriate for some repetitive and non repetitive 'generalised' functions. We see these in solitons, heaviside impulse functions and dirac functions amongst others.

Good evening Ed. Can you explain how something which does not cross zero for its duration, but remains at a constant level can have a frequency? I note the linked article also refers to PRR. The actual characteristics I gave are the bare minimum. In practice more may be needed for circuit design purposes.

Hello and welcome. Thinking up new ideas is to be encouraged, especially when you try to explain observed effects We call our propositions 'hypotheses' not theories which is what a hypothesis becomes after substantial verification. However it is always as well to make sure that you get your facts straight so deflection of light by magnetism? see here http://www.bbc.co.uk/education/guides/z996fg8/revision/4

Apologies mondie, I only looked at the worry over square brackets so I didn't notice you had displayed some. If your entire post #1 is confusing you, it is certainly comfusing me to unravel. I'm not sure why you are reading an electrical engineering book. Are you now studying electrical engineering? There was a long discussion on an electrical engineering forum where many engineers observed that although they learned calculus in college, they never used it in their working life. But they had to know calculus to pass their exams to become electrical engineers. Further complications for here are added because those studying electrical engineering at college (you will not meet those equations in school) are expected to have some basic physics so they understand that power is the rate of doing work and that energy is work times time. Further you have mentioned Ohms law for an inductor incorrectly. Your equation is Faraday's law of induction except that you have missed out the all important minus sign which shows that the induced voltage opposes the change in current. You also stated that you haven't taken a calculus course so not suprisingly you are struggling with the equations incolving calculus. I am now going to offer you an alternative life view called black box theory. Black box theory originated (I think) with electrical engineers, but it has spread to many disciplines. It is heavily used in electrical engineering and has the advantage that it can use both digital and analog techniques. Essentially you have a black box with an input and an output. The output is a well defined function of the input. But you don't worry how it works inside the box. The black box may be a physical device such as a breadmaker where the inputs are ingredients and the output is a loaf of bread; or it may be theoretical where the input is a number and the output is the square of that number. In the first example I have shown the basic box. I have added one extra line called control. This control allows me to vary the output that is produced from a given input. The second example is a nice double your money machine or scheme. The third example is the Las Vegas version. The fourth example takes a mathematical function and outputs the derivative of that function. The fifth example does the same for an integral, but also uses the control input to apply the boundary condions or the limits of integration. The final example is known as a two port network and is a fundamental building block in electrical circuit theory. So help us to help you by saying where you are coming from and where you want to go to. Are you interested in the Physics, the Electrical Engineering or the Mathematics, because, without black box methods, you need to get all of these right to succeed.

It's true that the thermite process now encompasses a wide variety of fuels. https://en.wikipedia.org/wiki/Thermite

You don't need a grenade for some fun spectacular burning and fuels. You can set fire to an iron rod if you heat it hard enough and then it will burn fiercely enough to cut through concrete and steel.

I am suprised at Schaum. They are usually pretty clear as they are designed for exam cramming. Difficult to comment on one I don't have. Do your square brackets look something like this? [math]\int\limits_0^1 {xdx} = \left[ {\frac{{{x^2}}}{2}} \right]_0^1 = \left[ {\frac{{{1^2}}}{2} - \frac{{{0^2}}}{2}} \right] = \frac{1}{2}[/math]

This discussion over tungsten filaments is a little esoteric, surely? The higher the filament temperature the whiter the light produced. Tungsten is used for filaments as it has the highest melting point of any metal a bit over 3400o K. However it has a positive coefficient of resistivity with temperature so as the filament heats up the resistance rises. This is fortutious as this means the current drops to a self limiting value. The filament resistance increases to nearly 20 times its cold (room temperature) value by the time it is near melting.

No problems we are all friends here and friends help when someone has had too much tequila.

Surely not because that would imply that the resistance of the conductor would disappear if you took the voltage away. The resistance of a material has nothing to do with the voltage applied to it in general. (Yes I know there are such things as VDRs)

No there can't be an infinite number of them whilst the particle is in the atom. There is a defined, finite, set of energy levels before any particular electron leaves the electron and the atom becomes an ion. At this point the energy spectrum of the electron becomes continuous, and therefore comprised of an infinitude of levels, although there is some debate as to whether it is actually continuous or made of incredibly finely divided levels.

I note you are seeking a basic explanation so There are two ways to approach this. The electrical engineer's approach which is offered at elementary level, even in Physics. Bender has already begun this. This is empirical (based on observation and experience) and simply accepts there is a property we call resistance that connects more basic electrical properties by Ohms Law. The physicists approach. However physicists do not (usually) work in terms of resistance. They study conductance, which is the reciprocal of resistance. This allows them to study why wires and other things conduct at all. So if we take Ohms Law V = IR and the observation that the power dissipated equals the product of the voltage and the current, P=IV we can generate two new equations. [math]P = IV = I(IR) = {I^2}R[/math] [math]P = IV = \left( {\frac{V}{R}} \right)V = \frac{{{V^2}}}{R}[/math] Now the power dissipated ends up as heat, so this tells us where the heat in your question comes from. The first equation tells us that the power dissipated is directly proportional to the square of the current and to the resistance. So if we maintain the current at a constant level and increase the resistance, more heat will be generated. However, and this is very important, Ohms Law tells us that you cannot specify all three of resistance, current and voltage. Once you have specified two of them the third is fixed (by Ohms law). So if we specify the current, and change the resistance, the voltage must vary to suit (goes up). But, as Bender pointed out, most electrical supplies (batteries, the mains and so on) have a fixed voltage. So if the voltage is fixed and we increase the resistance the second equation shows an inverse proportionality between power and resistance. So the power goes down if fix the votlage and increase the resistance, but the current varies goes down to suit. OK so this is all empirical. But why does things conduct at all and what is resistance? Well this question is not studied until university/college level physics and even today is not fully understood. There are several theories including the free electron theory and the band theory. Here is a non mathematical roundup. It is an observed fact that different materials conduct electricity to differing degrees. We distinguish three main categories Conductors Semiconductors Non Conductors In the free electron theory differning materials are able to release or free some (a very small proportion) of their electrons. These electrons are free to move about within the solid and become responsible for the ability of the material to conduct. Of course they leave behind much more massive atoms or ions, firmly locked in the lattice of the material. It is a good job these are not also free to move about or the material would fall apart! These free electrons 'drift' around in aimless or random fashion, moved on by thermal agitation. So there is no net movement in any direction. If we then impress a voltage difference the electrons are pushed in a preferred direction by this voltage. The greater the voltage, the more electrons are moved. A net movement of charge (electrons) constitutes a current so we have Yes you guessed it Ohms Law! The net current is proportional to the voltage. Now in a perfect crystal these free electrons are completely free to move. This is due to the perfectly regular nature of a perfect crystal exactly matching the quantum requirements for movement. Perfect crystals have zero resistance. But no crystal is perfect, certainly not the crystals making up a wire. There are several different imperfections, but all imperfections offer some resistance to free electron movement in their immediate environment. Imperfections include Impurities The fact that the wire is made of lots of small crystals joined together at random orientations so the moving electrons keep coming up against crystal boundaries. Thermal vibration distorting the perfect regularity of the lattice as the fixed ions/atoms vibrate about their mean positions. Does this help?

Financial? It's all done in brown envelopes.

Many thanks for taking the time to find this and make suggestions. Since, as I said in the OP, I don't have any connection to facebook I have no idea waht you mean by unfollow or any way to actually do it. If I was on their follow list why would it only happen with Chrome and not IE and now not (yet fingers crossed) with Firefox? Surely it must have been something on my computer, as SJ suggested. I consider myself lucky that I 'only' receive about two dozen trashy emails per day, but it is easy to spot the Wells Fargo, Nigerian Prices or Lisa Legs of this world and just delete them. I don't know Hanu and can't find anything useful on Google so I am reluctant to click on a link to an organisation (?) that has already added something unauthorised to my computer. This is no reflection on you, thanks agian for the link it is a step forward. But do you have any detail as to who hanu are and what their apps might be? I hope I have disposed of them, but I am pursuing this so others might benefit from anything dug up. +1 to you and to SJ for contributions.

+1 for introducing me to the word of the week. I have never heard of a cladogram or cladistics, but now I've not found it in any of my science dictionaries I'm sure the knowledge will come in useful someday. Plus some lukewarm praise for Mr Wiki who has at least heard of the words. Don't our biological colleagues have some interesting terms? I'm a strictly mechanical human.

No Chrome is no longer available for Windows XP.

For books of that size (but several times the cost) I would use that description for the Microsoft Press manuals available with every version of Windows. I'm really glad I don't have to buy them any more.

Yes of course, but the light given off from say a light bulb is generated by increased agitation of the tungsten lattice. Not directly by the (passage of) electric current or by the electric current itself. You would see the same light if you heated the wire with a blowtorch and passed no current whatsoever. That is what I meant by indirectly increasing the black body radiation (and its frequency)

I write formulae in MathType and copy/paste. So yes the symbols are available in MathType, but do not paste into this forum. Matrices have to be adjusted as well, but a lot of other stuff works just fine.

I don't know many wires that emit photons directly into the environment from electrical action. The resistance is internal to the wire. I am assuming you mean that due to the increased heating effect of current, as resistance increases the black body radiation from the wire will increase? But photons internal to the wire?

Being a simple soul, I like to look at it this way. n is the dimension of the vector space. n is number; no number is infinite. hence n is finite, however large. This is the old chestnut confusion of the difference between the cardinality of a set and the maximum value (or otherwise) of an element. Nice artwork by the way, it won't display those symbols here for me.

Photons or phonons?

The reasoning is inherent in the way you have set up the problem. You have a termination criterion viz a sequence terminates when 0 is reached, otherwise the process continues indefinitely. Thus all finite sequences terminate. (on 0) and all terminating sequences are finite. By similar reasoning an infinite sequence has not reached 0 and continues indefinitely without reaching 0 But you asked for the probability of reaching zero. I have been trying to offer more than just the answer to this question, but let's get the answer out of the way. So we must consider finite sequences and in particular how many finte sequences are there? Well consider this: In order to reach 0 a process must first reach 1 and then flip a tail on the next throw. The sequence to reach 1 must be finite as just noted above. But we can extend any finite sequence at all that goes ........WXYT, where at Y the sequence is at 1 on the ruler, by simply adding an H between the Y and the T thus WXYHT Which means the sequence is now at 1 on the ruler again after one more step So our new extended sequence is of the same form as before ie a single T off a termination to 0 on the ruler. This proceedure can be repeated indefinitely, each time extending the length of the sequence by one step. Since WXY is completely general, every finite sequence can be extended this way indefinitely. Which leads to conclude that the number of finite sequences can be considered infinite. Which leads to the conclusion that each one has zero probability.

OOps Chrome has gone but I can't now reload it since bigG steadfastly refuses to progress beyond the notice "This computer will no longer receive updates for Chrome" Incidentally I like REvo for uninstalling. That got rid of a deal of registry stuff and a bunch of 14 files (as you said would be left over, mostly appdata) Avast also offered to remove those files. Am using Firefox for now, seems OK so far, but I have had trouble in the past with Fox. One tip when rooting things out. Cleanup with something like ccleaner first. This gets rid of often many Gbytes of dross that your checker woud otherwise have to sort through. When you have finished clean up again with ccleaner. - it often finds leftovers like 'unused file extensions' and other rubbish exposed by the rootout. Thanks again for the help so far.