studiot

Can't think of any uses? How about battery powered door chimes? Magnetic braking? Magnetic lock? In fact anwhere that you want something mechanical held in or out of position. Any current going through an inductor generates a magnetic field. A constant direct current generates a constant magnetic field. So no, a/c is not 'normally used'. Further a/c can be steady or varying itself. But we can use that constant magnetic field for instance in focusing electron beams or anywhere that we require a magnetic field such as magnetic grapples, magnetic force between the poles of a D'Arsnoval meter and many many more. A final class of uses occurs in electronics where chokes (large value inductors) are used for smoothing purposes. What is you interest in the subject?

Are you thinking that the tension in the string has to be the same at all points? If so why? Are you thinking of this as a statics problem or a dynamics problem? You seem to want to introduce equilibrium which would make it a statics problem. But it is not a statics (equilibrium) it is a dynamics problem So if m2 is moving down m1 is moving up ie the string is taught. If m1 is moving up why should the net force on it be 10N ? As a dynamics problem do you know the law of conservation of momentum? Can you see how to apply it here?

What is your justification for saying this? Hint think very carefully about the question. Why would it mention friction if nothing moves?

You have quoted short extracts from what was presumably Maupertius' original writing. These do not describe the intended circumstances of transmission of the light. Perhaps a fuller account would do so (in French and/or English)? I only have access to latter day English descriptions which suggest that the intended circumstance was passage through only one medium at a time and that refraction on passing from one medium to another only resulted in a change of constant speed. That is Maupertius did not deduce Snell's Law. If that was the case then my comment about least time being equivalent to least distance still stands. It was also suggested that Maupertius changed (elaborated on) his proposal after Fermat and following discussion with Euler. So dates of statements might be of importance. Fermat's Principle itself was originally stated as a minimum condition, but we also now know that this should be an extremal condition since it is possible to devise light paths that are a maximum. For example some reflections at a concave elliptical mirror.

Open mind? to listen to a man who talks about (in the 20 seconds before your timestamp) magnets being better than electric because you don't destroy the charge when you extract energy One of the most basic laws of the universe is that charge can be neither created nor destroyed. Conservation of charge is even more fundamental than conservation of energy since it is unaffected by relativity, which conservation of energy is not. Then he goes on to claim that he get five times the energy out from his magnet than what he puts in, although he also claims he puts zero energy in so I suppose that is technically correct since 5 times nothing is still nothing. The he goes on to conjour upt the spirit world by separating the magnetic field form the magnetic vector potential. Talking of spirits Can I offer you a glass of alcohol free alcoholic drink? Oh and by the way To quote Martin Gardner, a well known journalist and mathematician reference https://www.csicop.org/si/show/dr._bearden_vacuum_energy

The only Tom Bearden I can find is an overunity crank who claims academic awards he doesn't have. So I ask you again. What do you mean by separate a magnetic field from its vector potential? Maths please.

Thank you for the reply, but I don't quite read the same line of reasoning into your extracts. In fact I am not quite sure what you are saying in several places. The 'action' Maupertius refers to is quite different from our use of the word today as the difference between kinetic and potential energies. Indeed the word 'energy' had yet to be formalised or even introduced. But Snell's law was the 'acid test' that distinguished between Newton's theory that of Young.

Many thanks for letting me know - I was quite unaware of it. +1 I must say, gees, the thinking in your posts is in no way impaired. Separating out the functions performed by a God as I sugested would help cut down the workload. If, for instance, you are thinking of God as a creator (yes I know there have been many discussion about this) then I could offer the 'scrabble theory'.

Not exactly sure what you mean by this? The magnetic vector potential (usual symbol A )is itself a vector field such that th emagentic field B is the curl of A. Alternatively wherever there is a current, the circulation of the magnetic field round that current is nonzero. Bu surely, asking to separate A from B is bit bit like asking to separate the direction field from its differential equation.

You asked the question and I responded by asking you to consider the material at the centre of the Earth, which is known to contain a high proportion of ferrous group elements because of the Earth's magnetic field. Since you didn't answer this, today I posted reliable material which shows your estimates of temperature in the Earth's core, is not high enough to produce a plasma in these materials.

Have you posted this material elsewhere, I'm sure I've seen something very similar somewhere? You also have a couple of related threads here that you seem to have abandoned following answers and comments by other folks?

So how long before the rest of us can expect answers to our comments? Of course I think mine were short but important.

Did you? I only posted it this morning. This was not an explanation of the terrestrial aurora, just a source of data. This was in response to your suggestion that the material in the Earth's core is compressed into a plasma.

Popular explanatory diagrams often show huge amounts of curvature, whereas in reality even Jupiter sized planets cause very mild levels of curvature. The original experimental proof of the curvature at the surface of the Sun sought a deflection of 1.6 seconds of arc for grazing light. The masses required to create Swartzchild conditions are many times larger. Perhaps Marcus could comment on this or Mordred (if he comes back). This is really their baby.

See my previous post.

Since you haven't come up with any answers, here are some 2018 facts and figures, quoted from the Aurora book I already mentioned. The Solar magnetic field permeates from inside the Sun through the photoshpere, the chromosphere and out into the Sun's outer atmosphere, the corona. So there you have it - ferrous plasma at 2000,000K. I bit out of your pay grade, I believe.

I salute your bravery in posting this topic. +1 I think it a good idea to distinguish between God as a creator and God as a meddler and/or manager. I see no reason for a God to provide all three functions.

I don't see any connection to the question here. Perhaps it would be a good idea to narrow down what you mean by 'electricity'. In particular what properties of electricity are you interested in? There are different models for different aspects of the subject so this would help to find the right one for your needs.

I thought you were satisfied with the previous posts. Anyway the story runs like this. Neither Fermat, nor Maupertius expressed their principles as integral equations. Light was known to travel at a finite speed and Fermat thought this to be constant. Fermat proposed that light follows the path that takes the least time to traverse. Maupertius was dissatisfied that time took precedence over space (distance) so he proposed that light follows the shortest path. Not suprisingly if light travels at a constant speed and takes the shortest time it's path must be the shortest path. So they are equivalent. That's really all there is to it.

Well there's a big difference between one tenth of a cubic metre and one tenth of a metre cubed. dm-3 should be one tenth of a cubic metre or (1 million cubic centimetres)/10 = 100,000 cubic centimetres. A decimetre cubed = (10cm x 10 cm x 10 cm) = 1000 cubic centimetres. and should really be denoted (dm)-3 But I should ask someone what was actually meant.

This is not clear. Do you mean mole per deci (metre)3 or mole per (decimetre)3 ?

Not quite. The constant current is only 'negative' because it is going against the chosen clockwise direction of mesh currents. If it was in the same direction as any of the circulating mesh curent it would be positive. Do you think the 5A and 7.5A sources oppose or add? What would happen if you reversed one of them?

Yes there are many basic methods of circuit analysis and they have point of similarity as well as differences. This includes node analysis, branch analysis, mesh analysis, Thevenin, Norton and superposition. After all they must come up with the same answers. It is common to take one basic simple circuit, using only simple componenets such as the one you posted, and compare the analyses by the different methods as you encounter them. There is also theory as to which method is the most efficient for a particular purpose, but that is not the reason for understanding them all. The point is that lecturers are also looking forward to the introduction of more complicated components and also the fact that most of our circuits ar AC not DC. The constant current generator is very important as it forms the basis of the model of the transistor that is used to include transistors into circuit. These methods you are learning have one common feature. They are based on the physical fact that if you take two points in a circuit, say A and B where you could separate the circuit into two halves by cutting through A and B, you can 'lump' the entire characteristics in one half into an equivalent cicuit. An equivelnt circuit is one which will behave the same way - there are always many, some more complicated, some simpler. Lump means collect all the components into one impedance (and/or source) that will behave the same way (equivalently). This is an incredibly powerful concept which has parallels in other areas of physics, eg mechanics but is much weaker there.

When using the mesh current method you should ahve been taught to replace the current source with an open circuit, since it has infinite impedance. Then you work on the revised circuit, maintaining the original mesh currents.

a speed of 100 metres per second! That's 225 miles per hour. How are you achieving this?