# Electric field without charge?

1. May 11, 2014

### mdn

hi all,
this question arises in my mind because, electromagnetic wave travel even in vacuum and we says that electromagnetic wave associated with electric field and magnetic field. now the questions is where is charge in medium, to say electric field?

2. May 11, 2014

### ZapperZ

Staff Emeritus
I wiggle some charge at position r=0. At r=20 km, you detect the EM field from it. Where is the charge?

This is not a trick question.

Zz.

3. May 11, 2014

### mdn

you hide that charge as well as electric field, how can i detect ?.

4. May 11, 2014

### Staff: Mentor

No one is hiding anything.

5. May 11, 2014

### mdn

It means only one person has eyes and all others blind!

6. May 11, 2014

### ZapperZ

Staff Emeritus
I have no idea what is going on here. You do know that you can detect EM radiation such as radio waves using an antenna, don't you? So what is hiding here?

You seem to thing that a region of space must locally have charge for there to be EM field. I'm trying to show you that that is false by demonstrating something which you already know and USE! Nothing is being hidden here!

Zz.

7. May 12, 2014

### mdn

Dear ZapperZ,
Thanks for your reply and bearing my such stupid question, but still i can,t believe how single wiggling charge (off course very large) spread it own information( in the form of EM wave) up to thousands of kilometre, without aids of medium.

8. May 12, 2014

### Staff: Mentor

Ignore the wiggling for a moment... Do you agree that if the charge were not moving it would be able to spread its static electrical field through space? Now, what happens to that field if you do move the charge?

9. May 12, 2014

### mdn

No! that's why in initiated such classical question. Inverse square law doesn't permit such lines of force to go large distance for example Van de Graaff generator, how long you feel the influence of such large charge in the form of lines of force.
and i believe due to movement of charge magnetic field has to play great role for spreading disturbances.

10. May 12, 2014

### Staff: Mentor

The inverse square law goes "hand in hand" with the lines of force extending straight outwards from the source to infinity. One is commonly used to derive the other in simple introductory presentations of electrostatics.

http://en.wikipedia.org/wiki/Inverse-square_law (note especially the diagram at the top of the page)

11. May 12, 2014

### ZapperZ

Staff Emeritus
This is puzzling. What is it that you "can't believe" here? What are you using as your "belief"? Don't Maxwell equations and experimental evidence trump your belief?

Zz.