How do we know light is electromagnetic wave?

[swansont]

Ok, thanks for clarifying. Now can you please say whether it is possible for a conductor to emit photons at a visible frequency without generating a corresponding amount of heat/infrared?

 

In principle, yes. That's what we've been saying for several posts now. The practical limit is that you can't get the oscillator you'd need.

 

What is the difference between using heat to oscillate electrons and using AC current? Is the issue getting the electrons to move without the nuclei vibrating? Isn't that what electricity is? Aren't photons the way that electrons release energy when they can't transfer it as kinetic momentum to adjacent particles?

 

Heat isn't AC current. Thermal agitation doesn't occur at one frequency. If you have questions on something other than the topic at hand, you really should do so in a new thread.

[lemur]

In principle, yes. That's what we've been saying for several posts now. The practical limit is that you can't get the oscillator you'd need.

But how can you have current, AC or otherwise that doesn't generate an appropriate amount of heat based on its resistance? If enough energy is flowing through the conductor to move the electrons at such a high frequency, wouldn't that conductor resist that current and generate the corresponding amount of heat?

 

Heat isn't AC current. Thermal agitation doesn't occur at one frequency. If you have questions on something other than the topic at hand, you really should do so in a new thread.

I wasn't asking that as an unrelated question. I was saying that the energy put into a wire as AC current is going to encounter a certain amount of resistance, which causes it to dissipate in the form of heat and/or EM emissions, no? So what I was asking was whether there is some difference between the resistance causing heat and that causing the radiation. In other words, a perfect conductor would not lose any energy to heat OR EM emissions. It would totally conserve the energy in the current, right? So whatever causes the conductor to resist current-flow must be responsible for BOTH heating and EM emissions, no? Then my question would be what determines how much energy goes into heat and how much goes into photons.

 

 

[davey2222]

But how can you have current, AC or otherwise that doesn't generate an appropriate amount of heat based on its resistance? If enough energy is flowing through the conductor to move the electrons at such a high frequency, wouldn't that conductor resist that current and generate the corresponding amount of heat?

 

 

I wasn't asking that as an unrelated question. I was saying that the energy put into a wire as AC current is going to encounter a certain amount of resistance, which causes it to dissipate in the form of heat and/or EM emissions, no? So what I was asking was whether there is some difference between the resistance causing heat and that causing the radiation. In other words, a perfect conductor would not lose any energy to heat OR EM emissions. It would totally conserve the energy in the current, right? So whatever causes the conductor to resist current-flow must be responsible for BOTH heating and EM emissions, no? Then my question would be what determines how much energy goes into heat and how much goes into photons.

 

An imperfect conductor would resist that current and generate the corresponding amount of heat. To get this issue out of the way let us use a superconductor so that Ohmic heating would not occur.

 

Now we are left with a zero resistance conductor carrying an AC producing an alternating magnetic field and producing radiating radio waves.

Edited February 5, 2011 by davey2222

[lemur]

An imperfect conductor would resist that current and generate the corresponding amount of heat. To get this issue out of the way let us use a superconductor so that Ohmic heating would not occur.

 

Now we are left with a zero resistance conductor carrying an AC producing an alternating magnetic field and producing radiating radio waves.

Ok, so if the AC current is vibrating the electrons without upsetting the atoms as a whole, and EM waves are getting emitted, what prevents those waves from getting absorbed into the conductor and generating heat that way? How can the electrons of a conductor be transparent to the same photons they are emitting?

[swansont]

But how can you have current, AC or otherwise that doesn't generate an appropriate amount of heat based on its resistance? If enough energy is flowing through the conductor to move the electrons at such a high frequency, wouldn't that conductor resist that current and generate the corresponding amount of heat?

 

I didn't say it would't generate the "appropriate" amount. R can be small, so the resistive losses would be small.

 

 

I wasn't asking that as an unrelated question. I was saying that the energy put into a wire as AC current is going to encounter a certain amount of resistance, which causes it to dissipate in the form of heat and/or EM emissions, no? So what I was asking was whether there is some difference between the resistance causing heat and that causing the radiation. In other words, a perfect conductor would not lose any energy to heat OR EM emissions. It would totally conserve the energy in the current, right? So whatever causes the conductor to resist current-flow must be responsible for BOTH heating and EM emissions, no? Then my question would be what determines how much energy goes into heat and how much goes into photons.

 

Yes, you were. Ohm's law is not what we're discussing. Saying a perfect conductor wouldn't lose energy to EM emission is flat-out wrong. Resistance is not responsible for the EM emissions we are discussing. It's not Ohm's law. Do I need to repeat that yet again?

 

Ok, so if the AC current is vibrating the electrons without upsetting the atoms as a whole, and EM waves are getting emitted, what prevents those waves from getting absorbed into the conductor and generating heat that way? How can the electrons of a conductor be transparent to the same photons they are emitting?

 

Why couldn't they be?

[lemur]

I didn't say it would't generate the "appropriate" amount. R can be small, so the resistive losses would be small.

I started another thread to discuss what causes energy to be dissipated as heat vs. EM waves.

 

Yes, you were. Ohm's law is not what we're discussing. Saying a perfect conductor wouldn't lose energy to EM emission is flat-out wrong. Resistance is not responsible for the EM emissions we are discussing. It's not Ohm's law. Do I need to repeat that yet again?

Is there anything constructive in your pushy language? Why is it wrong to call a conductor that conserves energy as current without releasing any of the energy as heat OR radiation a "perfect conductor?" If a conductor is losing energy to radiation, it wouldn't be conserving it perfectly, would it? Also, if you don't call whatever it is that is responsible for converting electrical current energy into photons "resistance," what do you call it? To me, "perfect current" would be current where all energy is retained within the electrons of the conductor. Any energy that is lost must be due to some form of "resistance," no? Or is this getting too close to assuming a medium for light?

 

Why couldn't they be?

Idk. Is there experimental evidence that a substance can emit photons that it cannot absorb? I would assume that if a frequency can be emitted then it can be absorbed, but maybe that is presumptive logic.

[swansont]

Idk. Is there experimental evidence that a substance can emit photons that it cannot absorb? I would assume that if a frequency can be emitted then it can be absorbed, but maybe that is presumptive logic.

 

Radio antennas actually work.

[alpha2cen]

According to energy conservation law, perfect conductor can not loose energy as radio waves.

So, superconducting conductor should not emit heat or radio waves, if not, it is against the energy conservation law.

The problem is the superconductor's superconducting range, i.e., at high frequency range it has superconductivity or not.

Edited February 5, 2011 by alpha2cen

[Cap'n Refsmmat]

lemur: As per rule 5, you should open a new topic for your questions, rather than hijacking another user's discussion. Otherwise I'll have to split off further discussion here.

[lemur]

lemur: As per rule 5, you should open a new topic for your questions, rather than hijacking another user's discussion. Otherwise I'll have to split off further discussion here.

I'm really confused. I don't see why these questions aren't contributing to sufficiently addressing the OP question. The issue is the relationship between electromagnetism and photons, right? Since black-body emissions are photons, I think it is relevant to address why/how resistance in a conductor results in both heat and EM emissions of increasing frequency (btw, I have started another thread to address this topic specifically). Then, the other issue is how AC current induces photon-emissions without causing heat, and whether this involves some form of resistance. Logically, it does from a macro perspective of energy-conservation in a conductor, but I still can't figure out what factor within the conductor-electrons could be responsible for resisting current in a way that directly generates photons. I assume, however, that this line of inquiry could be helpful in prompting others with more detailed knowledge to address the OP question more robustly. Am I obfuscating in from someone's point of view, though?

[Cap'n Refsmmat]

I'm really confused. I don't see why these questions aren't contributing to sufficiently addressing the OP question. The issue is the relationship between electromagnetism and photons, right? Since black-body emissions are photons, I think it is relevant to address why/how resistance in a conductor results in both heat and EM emissions of increasing frequency (btw, I have started another thread to address this topic specifically).

The question is how we know light is an EM wave. Conductor behavior has nothing to do with it. Anyway, the other topic will suffice now.

[davey2222]

lemur and alpha2cen,

 

A superconductor is defined as something that has zero resistance to the flow of current. Whether it loses energy or emits EM waves is not part of the definition.

 

So it seems that up to the current technology wise we cannot directly show that light is EM wave, or to produce light using purely electric-magneto method. Seems that light can only be produced with 'classical' means like burning (i.e. sun, flame, light bulb) and atomic excitation (i.e. LED, laser, fluorescent tubes).

[swansont]

lemur and alpha2cen,

 

A superconductor is defined as something that has zero resistance to the flow of current. Whether it loses energy or emits EM waves is not part of the definition.

 

So it seems that up to the current technology wise we cannot directly show that light is EM wave, or to produce light using purely electric-magneto method. Seems that light can only be produced with 'classical' means like burning (i.e. sun, flame, light bulb) and atomic excitation (i.e. LED, laser, fluorescent tubes).

 

I gave you an example of how charged particle beams do it. The acceleration is by bending the path rather than reversing the voltage.

[davey2222]

I gave you an example of how charged particle beams do it. The acceleration is by bending the path rather than reversing the voltage.

 

Since we can't do it electrically maybe we can do it mechanically.

 

I have an idea. Let us direct two electron guns at each other in a line of sight. Place in front of each gun a circular disk with slots cut into it to enable the electron beam to pass thru the slots as it rotates. The other disk is positioned such that when it allows its electron beam to pass thru, the other disk blocks its own electron beam, and vice versa. What we have now is an AC system. If we can have a large enough disks with many slots and make them rotate such that the resultant back and forth electron beams are in the THz range, it just might work. Crude I think.

 

Now place the whole setup in a vacuum. I predict the vacuum space between them would start to give off visible light as the setup is run. Any critique?

Edited February 5, 2011 by davey2222

[swansont]

For visible you need almost 10^15 interruptions/sec

[John Cuthber]

Synchrotron radiation can emit light as a direct effect of a magnetic field on a moving electron.

This is plainly an EM effect.

There may be others, but it only takes one to show that light is EM radiation.

[alpha2cen]

Temperature dependent black body radiation gave us some inquiry about light origin. Low temperature black body emits IR waves and high temperature black body emits UV or very short waves. And, heat transfer in the vacuum is only rely on this radiation. If light is electromagnetic wave, all heat transfer in the vacuum will be depend on electromagnetic waves. In conclusion, if light is electromagnetic wave, all objects will emit electromagnetic waves and it is not dependent on electron movement or magnetic field, and then the waves moving direction is high temperature to low temperature.

Edited February 6, 2011 by alpha2cen

[davey2222]

If we can have a big enough flywheel with mm slits cut into it and spun fast enough...

 

Can magnets be used to wiggle electrons flow in synchroton in the optical frequency rate?

 

Temperature dependent black body radiation gave us some inquiry about light origin. Low temperature black body emits IR waves and high temperature black body emits UV or very short waves. And, heat transfer in the vacuum is only rely on this radiation. If light is electromagnetic wave, all heat transfer in the vacuum will be depend on electromagnetic waves. In conclusion, if light is electromagnetic wave, all objects will emit electromagnetic waves and it is not dependent on electron movement or magnetic field, and then the waves moving direction is high temperature to low temperature.

 

I have thought about this. It seems that one doesn't need electric or magnetic field to generate EM waves, at least when it comes to heat. Is it accurate to state that EM wave is simply energy in its purest form?

[swansont]

If we can have a big enough flywheel with mm slits cut into it and spun fast enough...

 

Do the calculation… You need the period to be shorter than 10^-14 sec. At 1 mm separation the linear speed at the wheel edge needs to exceed the speed of light.

 

 

Can magnets be used to wiggle electrons flow in synchroton in the optical frequency rate?

 

You could but there's no need; the acceleration responsible for the EM emission is provided by curving the path. You use magnets with a linear accelerator.

 

 

I have thought about this. It seems that one doesn't need electric or magnetic field to generate EM waves, at least when it comes to heat. Is it accurate to state that EM wave is simply energy in its purest form?

 

Energy isn't a substance.

[davey2222]

Darn...physical limitations. How about if we use a flywheel made of diffraction grating? I suppose the result will be a broad spectrum of EM waves produced in the vacuum between the rotating flywheel.

[alpha2cen]

This is an example.

We fill water in the water tank, and shake it, at this time we can hear some sounds.

Next, we shout with large voice into the tank, at this time we find some waves are created on the surface of the water in the tank.

So we conclude that sound is made of water.

Is this any problem?