EGEE102: Energy Conservation and Envrionmental Protection

LESSON 1:
Energy and Society

	Objectives

1.2 Forms of Energy

6. Radiation, cont'd.

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Electromagnetic Spectrum

›	The “Electro-magnetic spectrum“ is a representation of the wide range of wavelengths of electromagnetic radiation.
›	Photons are associated with visible light, which accounts for only a very limited part of the electromagnetic spectrum.
›	A great discovery of the nineteenth century was that radio waves, x-rays, and gamma-rays, are just forms of light, and that light is electro-magnetic waves.

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As depicted in the image above, the lower the energy, the longer the wavelength and lower the frequency, and vice versa.

The reason that sunlight can hurt your skin or your eyes is because it contains "ultraviolet light", which consists of high energy photons. These photons have short wavelength and high frequency, and pack enough energy in each photon to cause physical damage to your skin if they get past the outer layer of skin or the lens in your eye.

Radio waves, and the radiant heat you feel at a distance from a campfire, for example, are also forms of electro-magnetic radiation, or light, except that they consist of low energy photons (long wavelength and high frequencies - in the infrared band and lower) that your eyes can't perceive. This was a great discovery of the nineteenth century - that radio waves, x-rays, and gamma-rays, are just forms of light, and that light is electro-magnetic waves.

About 20% of the electricity used in the US is used to produce visible light for lighting purposes.