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Physics, Astronomy & Cosmology / Re: What is the ratio between electric and magnetic field in electromagnetic waves?

« on: 01/03/2018 12:56:03 »

What is the ratio between amplitude of electric and magnetic field in electromagnetic waves?

In which unit of measure? In SI is c, as already said: ||E|| = c||B||; in other systems, the rate may not be c; in CGS - GAUSS the rate is 1: ||E|| = ||B||.
And this in the "far field" of the wave, that is far enough from the sources, or things become very complicated

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How can merely change the unit from SI to cgs

Things are different in electrodynamics because the magnetic field B is defined differently, it's not always a mere conversion from a value in a unit of measure to the other value in the other unit, sometimes even the equations are different. But your is a good question. Let's see the effect of this, that is the magnetic force on a moving charge q at velocity v in a field B which, for simplicity, is orthogonal to v.

1) In SI: F = q*v x B where "x" here stays for vectorial product. So, for an em wave in the void in the far field: ||F|| =  q||v||*||B|| = q||v||*||E||/c.

2) In CGS:  F = q*(v/c) x B. So, for an em wave in the far field:
||F|| =  q(||v||/c)*||B|| = q(||v||/c)*||E|| = q||v||*||E||/c

and the two are the same 

In the case of slowly rotating magnet, we can get amplitude of B much larger than amplitude of E when measured nearby.

Yes.

  But if we measure from adequately far distance, amplitude of B diminish quicker than E until their ratio approach a constant?

Yes. Do you remember what I wrote? Compute the wavelenght λ; how far from the source, let's say at distance r, you should evaluate the fields to be sure that r >> λ?
To compute the wavelenght remember that λ = c/f where f is the frequency. It's a trivial exercise.

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Physics, Astronomy & Cosmology / Re: Does a field require a source?

« on: 22/02/2018 18:49:35 »

However I don't like to call m "rest" mass because nowadays it's simply called "mass" (the so called "relativistic mass" is an  obsolete term and concept).

How far off the mark would I be if I interpreted this as saying: "rest" mass = total mass;

Ok, unless you give particular interpretations to "total" mass. Better to say "system" mass.

  "relativistic mass" = inertia? 

Do you like a concept of inertia which is different along different directions? Along the direction of the body's velocity you have a value of inertia, that is: γ³m, where γ is the gamma Lorentz factor:
γ = 1/sqrt[1-(v/c)²];
in the ortogonal direction you have a different value, that is: γm.
Conclusion: better not to talk about relativistic mass at all.
IMHO.

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Physics, Astronomy & Cosmology / Re: Does a field require a source?

« on: 18/02/2018 22:50:23 »

As I understand it, a field needs no source. A field just is. It's a sort of accounting or mapping tool that we can use to describe the universe. Every field exists everywhere, even if it has zero amplitude at specific places, or even everywhere.

You are saying, quite specifically, that a field (e.g. the electron field?)

"electron field" is something else, let's call it with a better name: electric (or electromagnetic) field generated by the electron.

 is the pre-existing entity – it needs no source.

The fact it needs a source doesn't mean it can't exists after being generated by it. You switch on a laser device: it generates a light beam; you switch off the device: the light beam keeps going towards its target.

If this is so, what meaning does it have to talk of the electron as the source of the field?

The ancient romans created the Adrian wall; the wall is still there, but the ancient romans don't exists anymore   

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Physics, Astronomy & Cosmology / Re: Does a field require a source?

« on: 17/02/2018 15:27:04 »

Would that theoretical construction you're proposing aim to alter the reference

It's not an "alteration": I have just specified (simple) initial conditions; the OP didn't specify them.

in view to make it more understandable?

The fact I used simple initial conditions is certainly in view of that.   

Sounds wonky but is theory here taking over fact?

Well, if we are still talking of a universe with ONLY two charges and nothing else, it's not simply theory, it's plain phylosophy   

But if we want to talk about something with some physical meaning and admit the existence of a little more than two charges only, i.e. at least a detector and a physicist  then the above simplification is acceptable.

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Chemistry / Re: How can pH be adjusted by using CaCO3 - calcium carbonate?

« on: 16/02/2018 17:23:54 »

What other simple chemical experiments are there used to alter pH of grapes?

If you add MgCO₃ or Mg(OH)₂ instead of CaCO₃, it helps you feel less muscular fatigue: athlets take sources of Mg²⁺ for that purpose  I don't know which will be the wine  final taste, however...

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Physics, Astronomy & Cosmology / Re: Do Photons exist?

« on: 15/07/2016 13:22:36 »

There is a lot of science that is based around the Photon, does the Photon exist?

Here is described how to prove in laboratory that photons really exists, that is, it's described a definitive proof of their existence:

http://people.whitman.edu/~beckmk/QM/grangier/Thorn_ajp.pdf

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Physics, Astronomy & Cosmology / Re: What would happen if I connected a pipe from the atmosphere into space?

« on: 05/12/2015 13:26:37 »

What would be the possible outcomes if a connecting pipe is kept on the boundary of atmosphere and space with one end in atmospheric layer and the other in the space..

A lot of flying collisions with the pipe  []

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Physics, Astronomy & Cosmology / Re: Does the mass of a system depend on its enthalpy or its free energy?

« on: 30/11/2015 08:01:32 »

I was inspired by this response in another thread (I added bold for emphasis for the purposes of my question):

...At the same time, using planet-wide temperature readings from NASA and other sources, one can see that the planet is warming up, or gaining thermal energy. This is coming from the Sun, and if energy is added to a system, then since E=mc^2, there is a corresponding increase in mass. Based on present data, this is probably adding a small amount of mass to the planet each year, of the order of 200 tonnes or so.

...

At the same time, the Earth is losing heat energy from its core as radioactive elements decay. Based on estimates of how much energy exits in this way, the mass loss is trivial though at about 16 tonnes per year...

Is the energy contribution to Earth's mass derived from the enthalpy (ΔH) of the system, or does it depend on the free energy (ΔG) of the system?

Recall: ΔG = ΔH – TΔS

My intuition says it has to be ΔH = Δmc², but if I'm wrong, I'll have to rethink some of my understanding of entropy and information.

I would say it's neither one nor the other but that it's ΔU, variation of internal energy. If volume and pressure doesn't vary, then it corresponds to ΔH (H = U + PV → ΔH = ΔU + VΔP + PΔV); but in general it's ΔU.

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Physics, Astronomy & Cosmology / Re: How do I explain general relativity to a six year old?

« on: 29/11/2015 15:44:28 »

When adding the speed of two protons, where v₁=v₂=c(1-x):
Total speed = (v₁+v₂)/(1+v₁v₂/c²)
=c((1-x)+(1-x))/(1+(1-x)(1-x))
=c(2-2x)/(2-2x+x²)
≈c-2c/x²

There is a little mistake here, the result should be ≈  c - cx²/2

≈ c - 2 mm/day

≈ c - 1 mm/day is my result, with your data.

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Physics, Astronomy & Cosmology / Re: Is time faster than the speed of light?

« on: 14/10/2015 13:51:24 »

To talk of "speed of something" we need that "that something" is a space. If we want to include other things which are not space and define the "speed of A" as dA/dt, then the speed of (proper) time is always 1: dt/dt = 1.

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Chemistry / Re: Why does silver develop a black tarnish patina?

« on: 20/09/2012 12:34:43 »

Sulfur is normally present in the aminoacids which make up the proteins, so we have a lot of it in our body. Probably different skin's metabolic processes of different people produces different amounts and different kinds of compounds containing sulfur (not hydrogen sulfide, this is not necessary to tarnish silver).

Another possibility is that you stay some time, at work or at home, near a source of gaseous sulfur compounds (you didn't specify if your sister lives and works close to you).

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Physics, Astronomy & Cosmology / How to define impulse of a rotating sphere?

« on: 10/07/2011 19:56:58 »

Thanks.
Then I would like to know average speed of all particles of the sphere(relatively of me).

If
ω = angular speed of rotation
R = sphere's radius

then, if I computed correctly the integral, it should be (3/16)πωR.

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Chemistry / Why does magnesium form magnesium nitride when it burns?

« on: 12/10/2009 19:53:41 »

Here it explain something:
http://www.chemguide.co.uk/inorganic/group2/reacto2.html

Why do these metals form nitrides on heating in air?

Nitrogen is often thought of as being fairly unreactive, and yet all these metals combine with it to produce nitrides, X₃N₂, containing X²⁺ and N^3- ions.

Nitrogen is fairly unreactive because of the very large amount of energy needed to break the triple bond joining the two atoms in the nitrogen molecule, N₂.

When something like magnesium nitride forms, you have to supply all the energy needed to form the magnesium ions as well as breaking the nitrogen-nitrogen bonds and then forming N^3- ions. All of these processes absorb energy.

This energy has to be recovered from somewhere to give an overall exothermic reaction - if the energy can't be recovered, the overall change will be endothermic and won't happen.
   

Note:  This is a bit of a simplification! In order to find out whether a reaction is feasible, you have to consider free energy changes and not just whether the reaction is exothermic or endothermic. If you don't know anything about free energy changes, don't worry about it. The simplification is valid in this particular case.

Energy is evolved when the ions come together to produce the crystal lattice. This energy is known as lattice energy or lattice enthalpy.

The size of the lattice energy depends on the attractions between the ions. The lattice energy is greatest if the ions are small and highly charged - the ions will be close together with very strong attractions. In the whole of Group 2, the attractions between the 2+ metal ions and the 3- nitride ions are big enough to produce very high lattice energies.

When the crystal lattices form, so much energy is released that it more than compensates for the energy needed to produce the various ions in the first place. The excess energy evolved makes the overall process exothermic.

This is in contrast to what happens in Group 1 of the Periodic Table (lithium, sodium, potassium, rubidium and caesium). Their ions only carry one positive charge, and so the lattice energies of their nitrides will be much less.

Lithium is the only metal in Group 1 to form a nitride. Lithium has by far the smallest ion in the Group, and so lithium nitride has the largest lattice energy of any possible Group 1 nitride. Only in lithium's case is enough energy released to compensate for the energy needed to ionise the metal and the nitrogen - and so produce an exothermic reaction overall.

In all the other cases in Group 1, the overall reaction would be endothermic. Those reactions don't happen, and the nitrides of sodium and the rest aren't formed.

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Physics, Astronomy & Cosmology / Re: The truth is out there, in pictures.

« on: 12/11/2007 13:15:36 »

The Hubble Ultra Deep Field

I think this represents what equates to a portion of the sky the size of a pinhead !!!

Each speck in this picture is a galaxy....each galaxy has about 100-300 BILLION Stars !!..and there's something like 100-300 BILLION Galaxies out there !!

<Mod Edit - picture removed as it's duplicated above and was causing slow loading for some people - Please see the Hubble Ultra Deep Field picture above>

Do you get it ?...can you even imagine such a thing ?...can you even fathom it ?


BEYOND COMPREHENSION !!

I agree with you; it's totally....can you help me to find a suitable term in english?

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General Science / How fast does a magnet attract ?..and other magnet questions !

« on: 06/03/2007 19:08:04 »

Dear Magnet Experts !
I'm not too sure how to word this...but....say you have a magnet ...is it always putting out pulling stuff ?...even when it has nothing near to attract ?...or does magnet joy only come into effect when a magnetizable thing comes within the magnets grasp !! ?
...also....how fast is the invisible stuff between the magnet and magnetizeable thing moving ?...do you know what I mean ? surely something is being pulled towards the magnet from the magnetizable thing...haw fast does it move ?

Do you mean which is the magnetic force's speed? It's c (light's speed).