When an AC signal is transmitted through a conductor, direction of flow of electrons is continuously alternated.

In wireless communication signal is transmitted through air, in this case which parameter of air is enabling current to propagate through it?

In conductor, electron from one atom moves to next, similar how electromagnetic wave move from one air atom to another?


Wireless communications signals do not propagate using air. They are electromagnetic waves that do not require a propagation medium. Consider that light reaches the earth from the sun without any propagation medium since the space between the sun and the earth is a near vacuuum. Light is simply a much higher frequency wave than communications signals. Radio astronomy relies on receiving electromagnetic waves from space at much larger distances than the sun without any propagation medium.

  • \$\begingroup\$ Not only are mediums (air, other gases, liquids, glass) unnecessary to EM waves, they tend to slow down their propagation. For example, EM waves travelling through air are 88km/s slower than through a vacuum. \$\endgroup\$ – Dan Laks Oct 9 '14 at 16:35
  • \$\begingroup\$ I got that. But without a medium how it is possible ? \$\endgroup\$ – tollin jose Oct 9 '14 at 16:49
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    \$\begingroup\$ @tollin: see Aether for a discussion of this historical fallacy. EM waves need no medium. \$\endgroup\$ – RedGrittyBrick Oct 9 '14 at 17:16
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    \$\begingroup\$ @tollin, sounds waves propagate by physically affecting the molecules of the gas or solid they move through. Electric and magnetic fields do not need to interact with matter to propagate. To get a more thorough treatment of the theory behind EM wave manifestation, I'd recommend posting a question on the Physics.SE. \$\endgroup\$ – Dan Laks Oct 9 '14 at 17:36
  • \$\begingroup\$ Technically EM fields are wave propagations through the medium of electric and magnetic fields (modeled as a continuous distribution of charge), hence why electron relaxing produces a photon. Though since electrons are mobile themselves then technically the medium is mobile, thus EM fields can travel in a vacuum. \$\endgroup\$ – Jarrod Christman Oct 10 '14 at 1:03

It used to be called the "ether". This is a name that satisfied the curiosity of folk that believed there must be a physical medium (of some form) that allows radio waves to propagate.

Radio waves inherently propagate thru space as does light (also a radio wave) and this propagation is determined by the physical properties of free space. Those physical properties are: -

  • Permittivity of free space at 8.8541878176 × 10−12 farads/metre
  • Permeability of free space at 1.2566370614 × 10−6 henries/metre

Air slightly modifies these physical quantities by a fraction as it happens.

If you took these two units and multiplied them together, then took the square root you'd get this number: 3.335641 × 10-9.

If you then inverted this number you'd get a velocity: -

299,792,458 metres per second - that happens to be the speed of light.

The "ether" is what light and conventional radio waves travel thru and comprises "stuff" that was probably created in the big bang and happens to have, what we call, permeability and permittivity. It's beautiful.

Which parameter of air is enabling current to propagate through it?

Current doesn't pass thru air to form a radio (electromagnetic wave) - fields pass thru the air/vacuum/medium that are called the E-field and the H-field.

how electromagnetic wave move from one air atom to another?

They don't rely on atoms or molecules or matter - they are slowed down and reflected/distorted by matter - EM waves (if they had an opinion) would want a vacuum.


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