# How do we visualize EM radiation?

• B
What is the best analogy to explain electromagnetic fields? I have seen the depictions of em radiation as perpendicular waves. Do we exist in a huge sphere of em radiation in which waves such as cell phone signals and radio broadcasts can be thought of as spherical ripples that emanate at the speed of light?

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ZapperZ
Staff Emeritus
What is the best analogy to explain electromagnetic fields? I have seen the depictions of em radiation as perpendicular waves. Do we exist in a huge sphere of em radiation in which waves such as cell phone signals and radio broadcasts can be thought of as spherical ripples that emanate at the speed of light?
You have a jumbled mixture of terminology here.

First of all, in your title, you used the term "EM radiation". To me, this means "light", as in electromagnetic wave, in which visible light is a part of. Whenever this is used, then this is a solution to the wave equation derived from Maxwell equations. This is where you get the E and B component of the EM wave being perpendicular to each other. So these are not usually called "perpendicular waves", but rather transverse wave, because the direction of motion of the wave is perpendicular to both the oscillating E and B field components of the wave.

But by saying that, it also means that ALL wave properties apply to this "EM radiation", including the relevant boundary conditions. A wave propagating in "free space" has different geometry than a wave coming off an antenna, and has a different geometry than a wave in a waveguide. You also have a difference between traveling wave and standing wave. An EM wave coming out of an antenna is not a "spherical ripple". It may have a circular wave fronts, and there may be some vertical spread in the wave, but most of the energy is directed horizontally due to the geometry of the source. An antenna is typically not a point point source, so it does not produce spherical waves. Again, boundary conditions.

So no, we do not exist in a "... huge sphere of em radiation ... "

Zz.

jtbell
Mentor
spherical ripples
The simplest form of electromagnetic radiation is "dipole radiation" produced by an oscillating electric dipole, e.g. a simple radio antenna. Here's an example of the electric field pattern:

As you can see, the pattern has a spherical aspect to it, but it's not uniform in all directions. The amplitude and direction of the fields that you observe depend on the direction of your location with respect to the dipole axis (vertical in this example).

A Google search for "dipole radiation" turns up many more pictures and animations. (This one is from the Wikipedia article on dipole antennas.)

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