electromagnetic waves

[nec208]

This web site seems to be a good web site explaining electromagnetic waves but some stuff there is not right.

http://science.hq.nasa.gov/kids/imagers/ems/waves2.html

Magnetism can also be static like a refrigerator magnet. But when they change or move together, they make waves - electromagnetic waves.

No waves are made with AC current not DC.If you change the AC it will make a wave .

Electromagnetic waves are formed when an electric field (shown as blue arrows) couples with a magnetic field (shown as red arrows).

No any electric current has a electromagnetic field around it and changing the AC makes the wave.All electric current or electricity have a electromagnetic field .

The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave. James Clerk Maxwell and Heinrich Hertz are two scientists who studied how electromagnetic waves are formed and how fast they travel.

If you want a wave change the AC.


Radio frequency or (RF) is a frequency of oscillation of AC wave ..Long wavelength uses low frequency and short wavelength uses high frequency..

 

[zz0468]

This web site seems to be a good web site explaining electromagnetic waves but some stuff there is not right.

Can you be more specific as to what you think is wrong? I looked, and it seemed pretty correct to me.

 

[rfradioconsult]

Geez I wasted all the years of education not to mention 40 years of work and I guess I should toss my IEEE membership.

 

[wlmr]

It appear I too will have to throw away all my books after this "enlightening" explanation of how AC cannot create electromagnetic waves. Power companies everywhere better start removing all those transformers they've been using for years - the OP's comments PROVE they can't work.

-

Sigh

Next I'll learn the Earth really doesn't revolve or some other profound piece of info.

 

[nec208]

Can you be more specific as to what you think is wrong? I looked, and it seemed pretty correct to me.

I did in the above quote!!

 

[nec208]

It appear I too will have to throw away all my books after this "enlightening" explanation of how AC cannot create electromagnetic waves. Power companies everywhere better start removing all those transformers they've been using for years - the OP's comments PROVE they can't work.

-

Sigh

Next I'll learn the Earth really doesn't revolve or some other profound piece of info.

I did not say AC cannot create electromagnetic waves.May be its just the article is put to gether bad at that web site.

 

[zz0468]

I did in the above quote!!

Oh dear... I really didn't want to have to do this...

No waves are made with AC current not DC.If you change the AC it will make a wave .

This statement makes no sense. If I read it literally, then it is factually incorrect. I really haven't a clue what you're trying to say here, and I doubt anyone else with any knowledge of the subject does either. It is essentially gibberish.

No any electric current has a electromagnetic field around it and changing the AC makes the wave.All electric current or electricity have a electromagnetic field .

I could say the same thing about this, too. Lets simplify this, shall we? All electric currents (AC AND DC) produce a magnetic field. Alternating current produces an alternating magnetic field.

If you want a wave change the AC.

Change the AC how? Do you have any clue what you're talking about?

Radio frequency or (RF) is a frequency of oscillation of AC wave ..Long wavelength uses low frequency and short wavelength uses high frequency..

This is the only statement in your original post that remotely makes sense, or is factually correct. And it only marginally makes sense. You clearly have a great deal to learn before you're ready to take on a NASA educational website, not the least of which is proper grammer.

 

[wlmr]

No waves are made with AC current not DC.If you change the AC it will make a wave .

No any electric current has a electromagnetic field around it and changing the AC makes the wave.All electric current or electricity have a electromagnetic field .

If you want a wave change the AC.

Radio frequency or (RF) is a frequency of oscillation of AC wave ..Long wavelength uses low frequency and short wavelength uses high frequency..

Your first 3 responses indicate that you think that unless you change the AC you don't get a EM field. As I recall, all my textbooks refer to AC as alternating current which by it's very definition is constantly changing.

The only one you approached being accurate about was the basic explanation of what RF is.

 

[nec208]

Oh dear... I really didn't want to have to do this...




This statement makes no sense. If I read it literally, then it is factually incorrect. I really haven't a clue what you're trying to say here, and I doubt anyone else with any knowledge of the subject does either. It is essentially gibberish.



I could say the same thing about this, too. Lets simplify this, shall we? All electric currents (AC AND DC) produce a magnetic field. Alternating current produces an alternating magnetic field.



Change the AC how? Do you have any clue what you're talking about?



This is the only statement in your original post that remotely makes sense, or is factually correct. And it only marginally makes sense. You clearly have a great deal to learn before you're ready to take on a NASA educational website, not the least of which is proper grammer.

I don't know if its my grammar thats gibberish or I don' understand electromagnetic waves ..

 

[nec208]

Your first 3 responses indicate that you think that unless you change the AC you don't get a EM field. As I recall, all my textbooks refer to AC as alternating current which by it's very definition is constantly changing.

The only one you approached being accurate about was the basic explanation of what RF is.

What voltage is coming out of it if its changing? Like how can the voltage go from 5 to 10 by it self .

 

[zz0468]

I don't know if its my grammar thats gibberish or I don' understand electromagnetic waves ..

What voltage is coming out of it if its changing? Like how can the voltage go from 5 to 10 by it self .

You just answered one of your own questions.

 

[nec208]

Okay reading the thread again its not making sense can some one here brake the points down here one by one .

Magnetism can also be static like a refrigerator magnet. But when they change or move together, they make waves - electromagnetic waves.



No waves are made with AC current not DC.If you change the AC it will make a wave .


Quote:
Electromagnetic waves are formed when an electric field (shown as blue arrows) couples with a magnetic field (shown as red arrows).



No any electric current has a electromagnetic field around it and changing the AC makes the wave.All electric current or electricity have a electromagnetic field .



Quote:
The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave. James Clerk Maxwell and Heinrich Hertz are two scientists who studied how electromagnetic waves are formed and how fast they travel.


If you want a wave change the AC.


Radio frequency or (RF) is a frequency of oscillation of AC wave ..Long wavelength uses low frequency and short wavelength uses high frequency..

and

What voltage is coming out of it if its changing? Like how can the voltage go from 5 to 10 by it self .

 

[zz0468]

Okay reading the thread again its not making sense can some one here brake the points down here one by one .

Sure.

Magnetism can also be static like a refrigerator magnet.

A refrigerator magnet creates a "static" magnetic field, meaning it's unchanging.

But when they change or move together, they make waves - electromagnetic waves.

An alternating current creates an alternating magnetic field. If that current is allowed to radiate an alternating electric field, it will create an alternating magnetic field. That alternating magnetic field will create an alternating electric field, which in turn creates an alternating magnetic field and on and on and on. An electromagnetic wave is born.

No waves are made with AC current not DC.If you change the AC it will make a wave .

This is YOUR words, and they make no sense.

Electromagnetic waves are formed when an electric field (shown as blue arrows) couples with a magnetic field (shown as red arrows).

This goes with the graphical depiction on the link you posted, and is a visual version of what I posted above.

No any electric current has a electromagnetic field around it and changing the AC makes the wave.All electric current or electricity have a electromagnetic field .

Again, your words, which don't make sense. ALL electric currents create a magnetic field. Period. An AC current creates an alternating magnetic field. You don't "change" the ac current. You generate it somehow (like in a transmitter).

The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave.

Perpendicular means 90 degrees from each other. So... if the electric field is vertical, the magnetic field is horizontal.

If you want a wave change the AC.

Your words, which are essentially meaningless. AC, by definition, IS changing. You don't need to change it again to generate an electomagnetic wave. What you DO need to do is use that ac current to induce an electric field, which is what an antenna does. That electric field induces a magnetic field , which induces an electric field, which induces a magnetic field... REMEMBER THAT?

Long wavelength uses low frequency and short wavelength uses high frequency..

A better way of saying this would be that high frequencies have shorter wavelengths than low frequencies.

What voltage is coming out of it if its changing? Like how can the voltage go from 5 to 10 by it self .

In an ac current, the voltage is constantly changing, from zero, to a positive peak, down to zero again, to a negative peak, back to zero, and it starts the cycle again. remember that word... "cycle". How does it do that? An oscillator will create an ac current like that. So will the alternator in your car (before it gets rectified to dc), or at an electric generating plant. It's not doing it by itself. Like I said before, it's being generated that way.

I can't break it down into simpler terms than that. You would be well served to pick up a book on basic electrical theory.

 

[mikewazowski]

This web site seems to be a good web site explaining electromagnetic waves but some stuff there is not right.

http://science.hq.nasa.gov/kids/imagers/ems/waves2.html

Unfortunately, I don't know what they're talking about but I'll try and bs my way through it to show you guys that I'm smarter then a NASA engineer.

Fixed it for ya....

 

[jhooten]

I don't know if its my grammar thats gibberish or I don' understand electromagnetic waves ..[/QUOTE]

Both. For the grammar portion let's look at this example:

No waves are made with AC current not DC.If you change the AC it will make a wave .

What you said is AC current does not make waves. What you meant to say was "That is incorrect" which would have been done by the addition of a punctuation mark like this:

No, waves are made with AC current not DC. If you change the AC it will make a wave.

Also not the addition of two spaces between the period ending the first sentence and the first letter of the second sentence. Also the deletion of the extra space between the e in wave and the period to end that sentence.

However a better way to express your point would have been:
That is not correct. Waves are made with AC current not DC. If you change the AC it will make a wave.

 

[loumaag]

Attention Please

Normally I would only step in if this was reported; however...

This topic indeed belongs in the general scanning forum, but only because it has been already read by people who may not have the knowledge to understand how far off the mark the OP was. To that end let me make a couple of things clear to the OP that should solve the problem. NASA is not wrong in the linked page. The interpretation of what is there is wrong.

Where on the NASA site was there any reference to DC (or AC for that matter)? There isn't any, so the comments reference to DC have nothing to do with the linked page.

The changing of either an electric current or a magnetic field will produce a change in the other, so the comment about electric fields being surrounded by magnetic fields although essentially correct does not point out any errors in the linked site. That is also applicable to the next comment made (about producing a wave by changing the AC.)

Now, let me say something else, this forum is not a place to take other web sites to task, especially when done so incorrectly. If someone wants to express an opinion about other people, sites, organizations, etc. (as long as it is kept clean), do it in the Tavern. Again, I am leaving this here only because of the confusion caused to other people due to the initial post. With any hope this topic will sink into history and not be a source of mistaken thinking for very much longer.

 

[kb2vxa]

Lou, I tend to agree with that last statement, a fitting end for a troll. The publicists at NASA don't write for those holding engineering degrees, they write for the general public. Unfortunately there are always a few pedants who pick everything apart and take it to task and we know who THEY are now don't we?

Oh BTW, you don't have to change AC because it changes all by itself now right? (;->)

"Now, let me say something else, this forum is not a place to take other web sites to task, especially when done so incorrectly."

Now let me invite you over to The Island Of Misfit Hams just to see how WE do it. (;->) (;->)

http://www.hamisland.net/forums/

 

[trooperdude]

The Island Of Misfit Hams

Isn't that redundant ???

 

[kb2vxa]

Well Troop, if you check us out you'll see we're anything BUT sexy. (;->)

 

[DaveNF2G]

I agree with those who take the OP to task for attempting to "correct" a technical website with misinformation.

However, I offer the following addition to the thread with the intent of helping the OP (and others) to understand better what is happening with AC versus DC, particularly regarding voltage changes as mentioned in the thread above.

Because an AC wave varies constantly from zero volts to its peak value (the top of each wave), measured AC voltage appears to be different from what you might expect if you know the peak value. There is a formula for this.

Peak voltage is the voltage at the top of each peak of the AC wave.

Average voltage is just what it sounds like - the equivalent DC voltage that would be measured if the AC wave produced exactly the average of all of the voltage values that exist throughout the wave. The forumula for calculating this is called "root-mean-square" or RMS. Average and RMS voltage are the same thing.

Peak voltage and average voltage bear a constant mathematical relationship to each other:

RMS = 0.707 Peak
Peak = 1.414 RMS

If you've been paying attention to the thread so far, you might have concluded that the magnetic field also has a range of values (although not expressed in voltage because that's not how we measure magnetism), and you would be correct. This oscillation in both the electric field and magnetic field is what makes electromagnetic coupling work, which enables such varying technologies as generators, motors, and radio transmission.