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Fig.11 - The electromagnetic spectrum radiation

radiation with longer wavelengths generally can penetrate through thicker solids.

Visible light, as we all know, is blocked by a wall. However, radio waves, having

wavelengths on the order of meters, can readily pass through concrete walls.

All things with a temperature above absolute zero emit radiation. Everything, your

body, your desk, your house, grass, snow, the atmosphere, the moon, they all emit a

wide range of radiation. The source of this electromagnetic radiation are vibrating

electrons that exist in every atom that makes an object.

The type of radiation emitted is determined largely by the temperature of the body.

Most "hot" objects, from a cooking standpoint, emit infrared radiation. Hotter objects,

such as the sun at ~5800 K, emits more energetic radiation including visible and UV.

The visible portion is evident from the bright glare of the sun; the UV radiation causes

tans and burns.

The emitted radiation strikes a second surface, where it is reflected, absorbed, or

transmitted (Figure 1.10). So emitted radiation can be:

 Absorbed. Increasing the internal energy of the gas molecules.

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