ELECTROMAGNETIC RADIATION

Energy which comes to us from the sun is transported in the form of waves known as electromagnetic energy. This combines electricity and magnetism such that setting up an electric current creates a magnetic field, and conversely, a magnetic field will set up an electric current. Electromagnetic waves, as with all waves, have properties of frequency, wavelength, and propogation speed which can be combined to form the relationship

c=lambda . f or propagation speed = wavelength · frequency.

(The property amplitude is not important in our discussion of EM radiation. Acoustic waves have ampitude which relate to power or volume)

In the case of EM radiation, the propagation speed (c) is a constant equal to the speed of light in a vacuum or 3 x 108 m/s. The speed of light according to Einstein is the maximum speed attainable by anything except space. To understand the speed at which light travels, imagine travelling 186,000 miles in one second! The relationship listed above translates to mean that frequency is inversely proportional to wavelength. Each frequency, therefore, relates directly to one and only one wavelength. The following chart gives the typical wavelengths and corresponding frequencies of important spectra of radiation.

THE ELECTROMAGNETIC SPECTRUM

The visible spectrum is relatively small with the darkest red at the long end of the scale to the darkest violet at the short. There are seven colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet forming the acronym ROY G. BIV". A typical wavelength for blue light is .47 microns and for red is .64 microns. (Remember these numbers for future use!)

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