Electromagnetic field theory. Q and A

[epepke]

Furthur, when we keep an iron piece in magnetic field then also it become magnetic. There is no applied energy to it. How then this energy come from?

This has already been explained to you, quite clearly. If a piece of magnetic tape magnetizes another piece of tape, the original recording degrades. That is where it comes from.

A more salient question is where the energy expended in trying to explain things to you goes.

 

[davefoc]

If gravitational potential energy (GPE) have some relation with propagation of energy?

Kumar,
I think the pendulum in your figure and your question go to complex issue that I don't understand in detail.

I believe that the amplitude of the pendulum's oscillation would gradually decrease even if it was swinging in a frictionless environment. This is because the pendulum would emit gravity waves. The energy lost through gravity waves would be infinitessmal compared to the energy of the swinging mass and the energy lost through friction in a typical real world situation, however.

The propagation of the gravity waves is similar to the propagation of an electro-magnetic wave in that gravity waves are believed to travel at the same speed as electromagnetic waves. This has been roughly verified through experiments and I believe it was predicted by Einstein.

One thing that has been theorized but not verified is that the gravity waves consist of discrete entities in the way that electromagnetic waves consist of photons. These discrete gravitational entities have been dubbed gravitons but nobody knows if such a thing exists.

 

[Kumar]

This has already been explained to you, quite clearly. If a piece of magnetic tape magnetizes another piece of tape, the original recording degrades. That is where it comes from.

A more salient question is where the energy expended in trying to explain things to you goes.

I am trying to know about magnet & iron. When we make a iron by rubbing magnet on it or keep iron in contact with magnet--iron aquire magnetic properties. I just want to know whether energy applied on rubbing or keeping iron near magnet is just equivalant to the magnetic energy as gained by iron piece or differant. I think in these cases, total magnetism remains the same in magnet but added to iron piece. In other words: whether total energy of magnet+ energy applied= total energy of magnet+ total magnetic energy in iron piece, is same or somewhat added/propagated.

 

[Kumar]

Kumar,
I think the pendulum in your figure and your question go to complex issue that I don't understand in detail....

Thanks. However in this case also, I want to understand whether energy applied on pendulum for raising it up & then releasing it(one time only) is just equal to energy on total swings, or it is more & so propagated. I mean:-

Total energy applied on pendulum(one time rise) = Total energy released by all swings as produced---is it ok or not or more?

 

[davefoc]

Kumar,
I am not sure I understand your question.

Under classical Newtonian type physics the situation is rather simple. The total energy in the system of the pendulum does not change after the initial energy to raise and release the ball is added to the system except for heat loss.

The nature of the energy changes as the ball drops potential energy is converted kinetic energy and as the ball rises kinetic energy is converted to potential energy. Throughout the process small amounts of energy are lost to friction which heat up the system of the pendulum (which might include the air the pendulum swings in). This heat is radiated away so that over time the energy of the pendulum system is lost to the surrounding environment.

 

[epepke]

I am trying to know about magnet & iron. When we make a iron by rubbing magnet on it or keep iron in contact with magnet--iron aquire magnetic properties. I just want to know whether energy applied on rubbing or keeping iron near magnet is just equivalant to the magnetic energy as gained by iron piece or differant.

Based on how you've stated it, the answer is yes.

I think in these cases, total magnetism remains the same in magnet but added to iron piece.

This isn't accurate. In the case of stroking, the energy comes from the stroking. In the case of putting a piece of iron next to another magnet and letting it sit (as in the case of print-through in magnetic tape), the original magnet weakens.

 

[69dodge]

Originally posted by Kumar
I am trying to know about magnet & iron. When we make a iron by rubbing magnet on it or keep iron in contact with magnet--iron aquire magnetic properties. I just want to know whether energy applied on rubbing or keeping iron near magnet is just equivalant to the magnetic energy as gained by iron piece or differant. I think in these cases, total magnetism remains the same in magnet but added to iron piece.

Yes, although "subtracted' might be better than "added." After all, the new and old magnets point in opposite directions, so their combined magnetic field is weaker than the original field was and therefore contains less energy. Where did the energy go? It did work on whoever brought together the iron and the magnet.

The two magnets now attract each other, so pulling them apart requires work to be done on them by an outside agent. More energy is required to pull them apart than was gotten when the magnetic field originally pulled them together, because---due to hysteresis---the iron is a stronger magnet now than it was before. And so their combined magnetic field after they are separated contains more energy than did the original magnetic field.

Energy is conserved. No "borrowing" is needed.

In other words: whether total energy of magnet+ energy applied= total energy of magnet+ total magnetic energy in iron piece, is same or somewhat added/propagated.

Same.

(Incidentally, physicists use the word "propagate" to refer to the transfer of energy from one place to another; they do not mean that the energy reproduces or multiplies in the way that plants do. When a plant "propagates," we can end up with more plants than we started with. When energy "propagates," we always end up with the same amount of energy as we started with; it's just in a different place.)

 

[Kumar]

Kumar,
I am not sure I understand your question.

Under classical Newtonian type physics the situation is rather simple. The total energy in the system of the pendulum does not change after the initial energy to raise and release the ball is added to the system except for heat loss.

The nature of the energy changes as the ball drops potential energy is converted kinetic energy and as the ball rises kinetic energy is converted to potential energy. Throughout the process small amounts of energy are lost to friction which heat up the system of the pendulum (which might include the air the pendulum swings in). This heat is radiated away so that over time the energy of the pendulum system is lost to the surrounding environment.

davefoc,

Thanks, First, when we rise the ball--our KE is converted to PE, second, when we release ball--PE is converted to just equal KE except some friction heat loss, third, this KE converted to PE on other side rise of ball-----so on. Ball stops swinging due to energy lost as heat by friction.

This defines that when we apply KE it is initially stored/conserved as PE equal to applied KE less friction/heat loss & if that PE is converted to KE--this KE will tend to convert in to PE again---the process goes on till all the applied KE is lost in friction as heat.

Right?

 

[Kumar]

Originally posted by Kumar
I am trying to know about magnet & iron. When we make a iron by rubbing magnet on it or keep iron in contact with magnet--iron aquire magnetic properties. I just want to know whether energy applied on rubbing or keeping iron near magnet is just equivalant to the magnetic energy as gained by iron piece or differant.

Based on how you've stated it, the answer is yes.

It means: our applied KE on rubbing or keeping iron near to magnet is conserved as PE in iron piece(less some heat loss).



This isn't accurate. In the case of stroking, the energy comes from the stroking. In the case of putting a piece of iron next to another magnet and letting it sit (as in the case of print-through in magnetic tape), the original magnet weakens.

When origional magnet weakens--means, its energy is transfered to iron piece. Where then our applied energy for keeping iron near to magnet goes?

 

[Kumar]

Yes, although "subtracted' might be better than "added." After all, the new and old magnets point in opposite directions, so their combined magnetic field is weaker than the original field was and therefore contains less energy. Where did the energy go? It did work on whoever brought together the iron and the magnet.

The two magnets now attract each other, so pulling them apart requires work to be done on them by an outside agent. More energy is required to pull them apart than was gotten when the magnetic field originally pulled them together, because---due to hysteresis---the iron is a stronger magnet now than it was before. And so their combined magnetic field after they are separated contains more energy than did the original magnetic field.

Energy is conserved. No "borrowing" is needed.Same.

(Incidentally, physicists use the word "propagate" to refer to the transfer of energy from one place to another; they do not mean that the energy reproduces or multiplies in the way that plants do. When a plant "propagates," we can end up with more plants than we started with. When energy "propagates," we always end up with the same amount of energy as we started with; it's just in a different place.)

Thanks, I think you already explained the awnser as I asked in my previous post to epepke.

All these indicated that nett result will be that applied mechnical energy(KE) on rubbing or on pulling is conserved as PE in iron piece as magnetic effect in it (less heat loss) & so mahnetic field in iron is due to our applied mechnical KE. Right?

 

[MRC_Hans]

Based on how you've stated it, the answer is yes.



This isn't accurate. In the case of stroking, the energy comes from the stroking. In the case of putting a piece of iron next to another magnet and letting it sit (as in the case of print-through in magnetic tape), the original magnet weakens.

I'm sorry but this is not correct. The original magnet does not weaken.

Think of it as a gravity well (although it is sort of a magnentism well). As you near the iron piece to the magnet, you sort of lower it into this well, you feel the iron being attracted to the magnet, and you absorb some energy letting it "run downhill". You might, with the proper mechanical arrangement, actually use this energy for something. When you are to remove the, now magnetic, iron piece, you will need toexpend some meore energy because the "magnetic well" has now become deeper.

I have already explained this, but Kumar will continue to ask if the answer is not the one he wanted it to be -

Hans

 

[MRC_Hans]

Kumar, I do not wish to try further to teach you basic physics. You are not an attentive learner. In my opinion, you are not interested in learning at all, only in trawling for bits and pieces, which, taken out of context, can be made to appear to support your beliefs.

Others may be more patient (or maybe they have not been at it as long as I have), and this I applaud, but I ask you now, in the nicest possible way, to seek knowledge elsewhere, and not snow this thread down with repeated, or irrelevant, questions, which I for one don't intend to reply to.

I repeat that the purpose of this thread is to serve as a tutorial in basic electromagnetism, and nothing else. Anybody is free to start similar threads on other subjects.

Hans

 

[Kumar]

Kumar, I do not wish to try further to teach you basic physics. You are not an attentive learner. In my opinion, you are not interested in learning at all, only in trawling for bits and pieces, which, taken out of context, can be made to appear to support your beliefs.

Others may be more patient (or maybe they have not been at it as long as I have), and this I applaud, but I ask you now, in the nicest possible way, to seek knowledge elsewhere, and not snow this thread down with repeated, or irrelevant, questions, which I for one don't intend to reply to.

I repeat that the purpose of this thread is to serve as a tutorial in basic electromagnetism, and nothing else. Anybody is free to start similar threads on other subjects.

Hans

Mr.Hans, You got irritated bit early. There can be differance of opinion/knowledge--and discussions here means to get differant views. You don't agree-what I say, I may also think accordingly. Differance in opinion is evident as you just replied. It is justified but sorry if you take it otherwise.

 

[Kumar]

davefoc, epepke,69dodge,others,

It is indicative by these discussions & may be of a gental knowledge concept that Applied KE on any substance can be converted & conserved into PE till it is used otherwise(subject to friction/heat loss) in it.

Now let us talk about forces & energies which are applied indirectly. These can be gravity,gravitational potential energy (GPE) , atmosphere interfearances, cosmic effects, plannetary influences, radiations etc. All these indirect effects may influence input & output similarities of any energy applied, conserved or used & so may propagate ot diminish the energy. Can you comment on this?

 

[The Don]

davefoc, epepke,69dodge,others,

It is indicative by these discussions & may be of a gental knowledge concept that Applied KE on any substance can be converted & conserved into PE till it is used otherwise(subject to friction/heat loss) in it.

Now let us talk about forces & energies which are applied indirectly. These can be gravity,gravitational potential energy (GPE) , atmosphere interfearances, cosmic effects, plannetary influences, radiations etc. All these indirect effects may influence input & output similarities of any energy applied, conserved or used. Can you comment on this?

Start another thread. This one's about Electromagnetic field theory

 

[Kumar]

Don,

Since these are continuing discussions & related to magnetic effects--I am unable to decide how to post in a seprate thread. Can you do it?

 

[MRC_Hans]

Kumar, I am asking you again, and still in a nice way: Kindly stop trying to hijack this thread. It has a specific purpose, and that purpose is not what you are following.

Hans

 

[Kumar]

Kumar, I am asking you again, and still in a nice way: Kindly stop trying to hijack this thread. It has a specific purpose, and that purpose is not what you are following.

Hans

Mr.Hans,

Since, this is your property & I am not a teritorist & you want to stop progress of some relevant concepts-- I may not post future questions & replies unless relevant to my already posted issues----as you know, I respect you. Thanks.

 

[Vitnir]

Sometimes I feel like writing letters to the editor of my local paper. In my latest contribution I compared the microwave EM radiation to the visible EM radiation of the sun saying that how can people be afraid of the base stations of wireless phones when the sun exposes us for more dangerous radiation (shorter wavelenghts). How true or false is that analogy if thats not too far from the subject.

It was published today, sweet Einstein its fun like hell to write letters to the editor.

And can base stations of wireless phones be compared to mobile phones in terms of EM radiation?

 

[MRC_Hans]

Vitnir:
Q: Sometimes I feel like writing letters to the editor of my local paper. In my latest contribution I compared the microwave EM radiation to the visible EM radiation of the sun saying that how can people be afraid of the base stations of wireless phones when the sun exposes us for more dangerous radiation (shorter wavelenghts). How true or false is that analogy if thats not too far from the subject.

A: False, I'd have to say (although no doubt basis for an interesting debate ). Here, it would probably be called a straw man. Solar radiation (at least the part that reaches the surface of the Earth) is in the range deep infra-red to near ultraviolet. This is several orders of magnitude shorter wavelengths than wireless phone signals.

True, those wavelengths are more energetic, all else alike, but the risks from them are very different. Also, of course, the fact that we have one dangerous kind of radiation should not make us complacent of another. That would be like looking out for trucks but ignoring person cars when crossing the road.

It was published today, sweet Einstein its fun like hell to write letters to the editor.

Q: And can base stations of wireless phones be compared to mobile phones in terms of EM radiation?

A: yes they can, although the problems differ somewhat (I assume you are talking about GMS cellphones and their base stations). Wavelengths are the same, but:

- The intensity of radiation is only on a level comparable to a phone when you are near a mast.

- But you are then exposed all the time, not just when you are talking.

- There is a special danger if you get within a few meters of the actual antenna (not mast). This can happen when they are mounted on rooftops etc.

Hans