1. Electromagnetic Spectrum
Unit 3.3

2. Wave Theory of Radiation
The description presented previously of light and other forms of radiation as electromagnetic waves traveling through space is known as the wave theory of radiation.

3. Wave Theory of Radiation
It is a spectacularly successful scientific theory, full of explanatory and predictive power and deep insight into the complex interplay between light and matter-a cornerstone of modern physics.

4. Wave Theory of Radiation
Around 1800, scientists were divided on the behavior of light. Some thought it traveled as a wave phenomenon while others claimed it was a stream of particles.

5. Wave Theory of Radiation
Experiments in the 19th century supported the wave theory. Yet with increasing technological advancements in equipment, physicists could not explain the discoveries in radiation and matter on atomic levels using the wave theory.

6. Wave Theory of Radiation
Changes had to be made and the modern theory of radiation is actually a hybrid of the wave and particle views, combining key elements of each in a unified theory.

7. Electromagnetic Spectrum

8. Electromagnetic Radiation
There is a relationship between the different types of electromagnetic radiation. The only characteristic distinguishing one from another is wavelength or frequency.

9. Electromagnetic Radiation
Radiation ranges from radio waves that have low frequency and long wavelengths to gamma waves, consisting of high frequency and short wavelengths.

10. Electromagnetic Radiation
Infrared radiation is tied in with heat. Shorter X-ray waves are best known for their ability to penetrate human tissue. Gamma rays are associated with radioactivity and damaging to living cells they encounter.

11. Electromagnetic Radiation
All these spectral regions, including the visible spectrum, collectively make up the electromagnetic spectrum. All are basically the same phenomenon and move at the same speed.

12. Electromagnetic Radiation
If you note that as frequency increases, wavelength decreases. The scale is marked by factors of 10 – each is 10 times greater than its neighbor.

13. Electromagnetic Radiation
This type of scale, called a logarithmic scale, is often used in science to condense a large range of some quantity into a manageable size.

14. Electromagnetic Radiation
Only a small fraction of the radiation produced by astronomical objects actually reaches Earth’s surface, because of the opacity of our planet’s atmosphere.

15. Electromagnetic Radiation
In actually, parts of the atmosphere are opaque and some parts are transparent. This is due to the gases present. Certain atmospheric gases absorb radiation very efficiently at some wavelengths.

16. Electromagnetic Radiation
For example, water vapor and oxygen absorb radio waves having wavelengths less than about a centimeter, while water and carbon dioxide are strong absorbers of infrared radiation.

17. Electromagnetic Radiation
Ultraviolet, X-ray, and gamma ray radiation are completely blocked by ozone layer high in Earth’s atmosphere.

18. Electromagnetic Radiation
A passing, but unpredictable, source of atmospheric opacity in the visible part of the spectrum is the blockage of light by atmospheric clouds.

19. Electromagnetic Radiation
In addition, the interaction between the Sun’s ultraviolet radiation and the upper atmosphere produces a thin, electrically conducting layer at an altitude of about 100 km.

20. Electromagnetic Radiation
This ionosphere, as this layer is known, reflects long wavelength radio wave as well as a mirror reflects visible light.

21. Electromagnetic Radiation
In this way, extraterrestrial waves are kept out, and terrestrial waves are kept in - such as those produced by AM radio stations.

22. Electromagnetic Radiation
The effect of atmospheric opacity is that there are only a few spectral windows (windows of transparent atmosphere).

23. Electromagnetic Radiation
We can study the universe from ground level in areas where radio waves and visible light are dominant since opacity is low.

24. Electromagnetic Radiation
In parts of the infrared range, the atmosphere is partially transparent, so we can make certain infrared observations from the ground.

25. Electromagnetic Radiation
Moving to the tops of mountains, above as much of the atmosphere as possible, improves observations.

26. Electromagnetic Radiation
In the rest of the spectrum, the atmosphere is opaque: UV, X-ray, and gamma ray observations can be made only from above the atmosphere, from orbiting satellites.