Electromagnetic Radiation 

 

Electromagnetic Spectrum

   The first thing you need to remember is that in physics all forms of electromagnetic radiation is "light".  The everyday use of light is what we call the visible light spectrum (which turns out to be a tiny part of the entire light spectrum).  

 The Electromagnetic spectrum starts with high frequency light on left , starting with gamma radiation, then x ray followed by ultra violet.  These are also the high energy electromagnetic radiation, because light can not travel faster 3 x 10^8 m/s, light expresses it energy in it frequency, high frequency high energy.  

After Ultra violet is the visible light spectrum, which is 1/100th the size of x-ray spectrum.  As a matter of of fact the visible light spectrum is the smallest region on the entire electromagnetic spectrum, but everything you see is a result of the this small range (consider what the world would look like if you could see into the ultra violet, it turns out certain incests and chickens can but only a very limited range) 

After the visible light spectrum is the low frequency, low energy light;  Infrared, microwave, and radio waves, makes up this region.  Energy and wavelengths are inversely proportional, meaning High energy small wavelengths, low energy long wavelengths.  Some of the wave lengths in this region are so long that wrap themselves around mountains even planets (thats the reason we use radio waves for radio and television signals). 

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Self Propagating wave

Electromagnetic radiation is a phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic "unit" of light and all other forms of electromagnetic radiation.

Definition Provided by Wikipedia

Wave propagation is any of the ways in which waves travel.

Self propagation may occur in a vacuum (with out a medium) as well as in a material medium. Most other wave types (non self propagating wave e.i mechanical waves) cannot propagate through vacuum and need a medium (air water, rock, etc....) to exist.

 Definition provided by Wikipedia

Oscillating Electromagnetic fields

    We saw that a moving charge creates a magnetic field, but what if the motion of that charge is a simple back and forth direction?   

     Well if we apply what we know about simple harmonic motion (motion described by sine and cosine functions) and the creation of magnetic fields due to moving charges (current in one direction creates a curl in one direction, if the current is flipped the field curls in another direction), you would find that the magnetic field would oscillate.  Well along comes a physics by the name of James Maxwell (many consider Maxwell to be one of the great physicists of all time, up there with Newton, Galileo, Einstein, Bohr, and Schroedinger), he noticed that a changing magnetic creates a changing electric field.  

     Because of Maxwell's discorvery, we know of this relationship, Moving a charge (or a current) back and forth creates a changing magnetic field, but a changing magnetic field creates a changing Electric field, which in turn creates a changing magnetic field, which in turn creates a changing magnetic field, etc.... . So this discovery was ground breaking we see that the magnetic and electric fields supported each other, re-enforcing each other, needing only the other to "survive". This is why Light is called a self propagating wave. 

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