Is it field?Danger said:Light is an electromagnetic field. It is simply our way of identifying the visible (and near-visible) segment of the EM spectrum. There are several arbitrarily defined segments such as microwave, radio, X-ray, gamma, IR, etc.. Light is generally considered to be the part that we can see.
Yes. There is one and only one difference between, say, and EM wave at microwave frequencies and that of a red beam of light is the frequency of the waves. They are exactly the same in physical properties and makeup.scientist91 said:Is it field?
pmb_phy said:Yes. There is one and only one difference between, say, and EM wave at microwave frequencies and that of a red beam of light...
scientist91 said:If you say that the light is field, then I will make electromagnetic induction with light and get current in closed circular loop.
Can you give me some link or picture?ZapperZ said:And you do! People who work in designing accelerator cavities have to deal with wall currents due to the the changing B fields. That is why you have lossy material.
Zz.
scientist91 said:Can you give me some link or picture?
So let's conclude the light is electric and magnetic field, right?
Due to the high frequency of a light wave the light would not be able to penetrate inside a conductor. Same thing with x-rays.scientist91 said:If you say that the light is field, then I will make electromagnetic induction with light and get current in closed circular loop.
Look man, if you say that the light is both part of magnetic and electric field, then, the photons "are moving" (so the magnetic field is moving), so it will produce current inside the conductor, right?pmb_phy said:Due to the high frequency of a light wave the light would not be able to penetrate inside a conductor. Same thing with x-rays.
You wanted a picture, right? Draw a picture of an EM wave and you have by neccesity drawn a picture of light.
What part of "Light is an EM wave" don't you understand?? Its a pretty simple idea.
Pete
scientist91 said:Look man, if you say that the light is both part of magnetic and electric field, then, the photons "are moving" (so the magnetic field is moving), so it will produce current inside the conductor, right?
Why the electrons can't move so fast when the magnetic field of the light is moving so fast? Practically, when you move magnetic field faster, so the electrons in the conductor are moving faster, so the current is stronger.Xezlec said:It does produce a current. YES. Light does produce an electric current in any conductor it hits. Indeed.
But light has a very high frequency. So because the frequency is so high, the "electrons in the conductor can't move fast enough". So the current is very very very very small.
That's an oversimplification, but I don't know what else to say that will be understood.
scientist91 said:Why the electrons can't move so fast when the magnetic field of the light is moving so fast? Practically, when you move magnetic field faster, so the electrons in the conductor are moving faster, so the current is stronger.
Suppose you are pushing a child in a swing. Let's say you give a push every two seconds, to increase its amplitude. What would happen if you gave a push every tenth of second? The swing wouldn't move much. Make the experiment.scientist91 said:Why the electrons can't move so fast when the magnetic field of the light is moving so fast? Practically, when you move magnetic field faster, so the electrons in the conductor are moving faster, so the current is stronger.
I think you have wrong understood it. Look, I made that experiment. So if I push with 0.1sec (with same power) when I will get to 2 sec (0.1*20) so the swing's moving speed will be so fast, 20 times more then once in 2 seconds.lightarrow said:Suppose you are pushing a child in a swing. Let's say you give a push every two seconds, to increase its amplitude. What would happen if you gave a push every tenth of second? The swing wouldn't move much. Make the experiment.
But man, when you practically moving magnet among conductor, it will induce current inside of the conductor. When you move the magnet very fast so the electrons are moving very fast, right?Xezlec said:It's hard to explain in such simple language. Pick up a spring. Hold it by one end. Move it up and down slowly. Now try moving it faster, and faster, and faster. Eventually the spring won't bounce very much anymore because you're shaking it too fast. It can't keep up.
Electrons have mass, and they also have other things "holding" them. They are stuck in a "soup" of other electrons, so they can't just move as fast as you want.
scientist91 said:But man, when you practically moving magnet among conductor, it will induce current inside of the conductor. When you move the magnet very fast so the electrons are moving very fast, right?
scientist91 said:So, when you move the magnet very fast among conductor in closed circular loop you create stronger current. But what will happen if the light wave oscillate hundrets of trilions times per second? The electrons will not move, but why?
Can understand what actually happens with the electrons. They must move when there is presence of magnetic field, so when you move the magnet very frequently you get current, still I can't understand, what actually happens when there is presence of light with high frequency.rbj said:you're not listening. whether you are generating light (or any other E&M field) or receiving such a 'transmission", electrons (or some other charged object) are, at least in a probabilistic sense, moving back and forth. even at trillions of Hz. eventually frequencies get so high that matter doesn't have much ability to deal with it. i think your DNA would get messed up if you were exposed to enough gamma or cosmic radiation.
but 91, you just need to accept that visible light is just another set of frequencies in the broad EM spectrum. that's what several other people are trying to confirm to you.
As we are trying to make you understand (I tried with the example of the swing but I had no success!), since electrons have a non-zero mass and so have inertia, if you try to move them with an oscillating force which frequency is too high, they cannot follow the movement of the force; just because of their inertia, at the time they have started moving in one direction, the force has already changed direction, so they don't have time to follow its movement. Try to figure it out.scientist91 said:Can understand what actually happens with the electrons. They must move when there is presence of magnetic field, so when you move the magnet very frequently you get current, still I can't understand, what actually happens when there is presence of light with high frequency.
Ok now I understood it, but I have one more question, are the electrons moving in conductor (with current), moving like they move in nuclei (spinning)? When they are excited and gain energy and unbound from the atom, they release the excess of energy?lightarrow said:As we are trying to make you understand (I tried with the example of the swing but I had no success!), since electrons have a non-zero mass and so have inertia, if you try to move them with an oscillating force which frequency is too high, they cannot follow the movement of the force; just because of their inertia, at the time they have started moving in one direction, the force has already changed direction, so they don't have time to follow its movement. Try to figure it out.
But notice, you would have the same exact situation with every object with non zero mass, accelerated with a force with constant amplitude but increasing frequency: in the simpler case of a free object, the amplitude of its oscillations decreases as the force's frequency increases.
When they are excited and gain energy and unbound from the atom, they release the excess of energy?
Sojourner01 said:No. For a start, you've got this muddled:
Electrons in atoms release energy when they drop through energy levels. They absorb energy to gain energy levels, and eventually dissociate entirely.
Even so, this isn't what happens in a conductor. Electrons in metals move as though they are free, even though they are in fact still in the potential of the nuclei. This property is what makes metals metallic; this is what metallicity is. The mechanics of this are complicated and I don't fully understand them myself, suffice to say it's to do with the periodic nature of the nuclear potential wells.
when they are excited or forced from the magnetic field! How do they release that excess of energy when they are moving in the conductor?Sojourner01 said:What excess of energy?
I understand you. But trust me, it is very hard for me to translate and understand all of the posts that you're writing me. I am very very thankful for your effort and patience, trying to explain me some things. So before I post here I am searching everywhere, so if I didn't find answer, I am writing here on this forum. So I just want to ask you if you can, to draw some picture of the actual spinning of the electrons, to understand better. I am going to ask you again. Are the free electron's movment is like when they are spinning around nuclei, or they are just moving straight, across all of the atoms? Thank you very much.Sojourner01 said:Moving electrons are currents. Currents incur energy losses as heat through electrical resistance. The mechanism behind this is due to i) defects in the conductor and thus in the periodic potential ii) quantised vibrations of the atomic lattice called phonons. I can't imagine I could communicate the nature of the electron-phonon interaction to you at your level of knowledge; not least because I don't understand it very well myself.
I must say this line of questioning is becoming tiresome. I'd very strongly advise you to read books like numerous helpful members have suggested. We are not your teachers; specific conceptual problems anyone here will be happy to answer in the context of a student seeking additional dialogue from elsewhere.
Ok, thank you.Mentz114 said:Very briefly, electrons in a metal can have certain energy levels that fall in the conduction band. These electrons can 'hop' from atom to another to make a current. But it's not as simple as classical particles moving. You need quantum mechanics to understand it properly, which I don't claim I do.
scientist91 said:Can somebody explain better?
But is there any small current or something? And can the light itself to be current, because it have part of electric and part of magnetic field?rbj said:look at it this way, 91: imagine that you and i are standing some distance apart and facing each other. you're holding a positive charge and i am holding a negative charge and that we both are restricting our charges so they cannot move toward each other but they can move up and down and left and right (just not forward or backward). so i move my charge up a meter. since your charge is attracted to mine, your charge also wants to move up a meter and you allow that. then i move it down and your charge follows it down. now i move it to my right (your left) and your charge moves toward your left. then to my left (your right) and your charge follows it.
now i move my charge up and down repeatedly and your charge follows it up and down. that is an electromagnetic wave that originated with me moving my charge around and that wave moved toward you (at the speed of propagation of E&M waves which is "c") and caused your charge to move. in a very real sense, my moving charge is a "transmitting antenna" and your moving charge is a "receiving antenna". if, somehow, i could move my charge up and down a million times per second, you could tune your AM radio to 1000 kHz and hear a signal (a silent carrier). if i could move it up and down 100 million times per second, you could tune it in with your FM radio just between the 99.9 and 100.1 settings (provided no other stations were close by). if i could move it up and down 500 trillion times per second, you would see it as a blur of orange colored light. now i can't move it up and down an entire meter 500 trillion times per second because the speed of that movement would exceed c. but i can have a whole pile of like charges and move them up and down maybe 10 microns at a frequency of 500 trillion Hz. that is what happens in a transmitting antenna.
that is what light is (from a wave-property perspective) and it required no medium for these waves to travel. they just are there because unlike charges attract and like charges repel - there need be no medium in between for that to happen.
there are other phenomena that light exhibits that make it appear like it's made up of particles (such as the photo-electric effect). seems like a contradiction, but both behaviors are exhibited by light and all the physics is, is an attempt to coherently describe and explain both demonstrated properties. light, which is EM radiation at about 500 GHz, has both wave-like and particle-like behavior.
The electric and magnetic fields in EM radiation are sourceless. There is no charge, therefore no current. The electric field can induce a current in an antenna. Read rbj's post carefully.But is there any small current or something? And can the light itself to be current, because it have part of electric and part of magnetic field?
scientist91 said:But is there any small current or something? And can the light itself to be current, because it have part of electric and part of magnetic field?
Ok, I understand, but what is the shape of the magnetic field of the electron? Can that electron be excited of its own magnetic field?Xezlec said:Current means charges moving. Light = fields moving, but not charges moving. When light hits a conductor, there is a tiny current.
Xezlec said:It's hard to explain in such simple language. Pick up a spring. Hold it by one end. Move it up and down slowly. Now try moving it faster, and faster, and faster. Eventually the spring won't bounce very much anymore because you're shaking it too fast. It can't keep up.
Electrons have mass, and they also have other things "holding" them. They are stuck in a "soup" of other electrons, so they can't just move as fast as you want.
tell me what actually happens? Why with the high frequency there can't be induced current? In normal magnetic field when you move the magnet from the on side of the coil that is + and from the other side - and when you pull back the place where the + was now is - and the place where the - was now is +. So with high frequency the + and - can't change so fast or what?rbj said:look at it this way, 91: imagine that you and i are standing some distance apart and facing each other. you're holding a positive charge and i am holding a negative charge and that we both are restricting our charges so they cannot move toward each other but they can move up and down and left and right (just not forward or backward). so i move my charge up a meter. since your charge is attracted to mine, your charge also wants to move up a meter and you allow that. then i move it down and your charge follows it down. now i move it to my right (your left) and your charge moves toward your left. then to my left (your right) and your charge follows it.
now i move my charge up and down repeatedly and your charge follows it up and down. that is an electromagnetic wave that originated with me moving my charge around and that wave moved toward you (at the speed of propagation of E&M waves which is "c") and caused your charge to move. in a very real sense, my moving charge is a "transmitting antenna" and your moving charge is a "receiving antenna". if, somehow, i could move my charge up and down a million times per second, you could tune your AM radio to 1000 kHz and hear a signal (a silent carrier). if i could move it up and down 100 million times per second, you could tune it in with your FM radio just between the 99.9 and 100.1 settings (provided no other stations were close by). if i could move it up and down 500 trillion times per second, you would see it as a blur of orange colored light. now i can't move it up and down an entire meter 500 trillion times per second because the speed of that movement would exceed c. but i can have a whole pile of like charges and move them up and down maybe 10 microns at a frequency of 500 trillion Hz. that is what happens in a transmitting antenna.
that is what light is (from a wave-property perspective) and it required no medium for these waves to travel. they just are there because unlike charges attract and like charges repel - there need be no medium in between for that to happen.
there are other phenomena that light exhibits that make it appear like it's made up of particles (such as the photo-electric effect). seems like a contradiction, but both behaviors are exhibited by light and all the physics is, is an attempt to coherently describe and explain both demonstrated properties. light, which is EM radiation at about 500 GHz, has both wave-like and particle-like behavior.
scientist91 said:tell me what actually happens? Why with the high frequency there can't be induced current? In normal magnetic field when you move the magnet from the on side of the coil that is + and from the other side - and when you pull back the place where the + was now is - and the place where the - was now is +. So with high frequency the + and - can't change so fast or what?
