The Nature of Light

1. The Nature of Light Students will describe the electromagnetic spectrum and each type of light in it. Students will also discuss the visible light spectrum and the colors in it. Students will also explain how colors are added and subtracted when discussing light and pigments

2. The Speed of Light • Light travels at 3x108m/s, whereas sound only travels at about 340 m/s • That is 880,000 times faster than the speed of sound!!!! • 3x108 = 300000000 • Lightning vs thunder – which is faster?

3. The Speed of Light • Light does not require a medium in which to travel (it is not a mechanical wave) • Light travels fastest in a vacuum (which isn’t considered a medium) • The denser the medium, however, the slower light will go

4. The Electromagnetic Spectrum All forms of light are part of the EM spectrum • Radio Waves – have the longest wavelength • Microwaves (not the oven, but IN the oven) • Infrared – associated with heat • Visible light – what our eyes are able to see • Ultrviolet – beyond violet • X-Rays – discovered in the early 1900s • Gamma Rays –have the shortest wavelength

6. Radio Waves • Includes AM and FM waves • Longest wavelength and lowest frequencies • Low energy waves • Used for broadcasting radio signals • Television signals are also broadcast • Satellites often bounce the signals

7. Microwaves • Shorter wavelengths than radio waves • Used IN microwave ovens • Radar – used for detecting speed and location of objects

8. Infrared • Even shorter wavelength than microwaves • Carries more energy, as well • Infrared light causes particles to vibrate faster, and faster vibrating particles is associated with heat • Your eyes can see infrared, but special glasses and imaging software can detect heat patterns

9. Visible Light • Very narrow range of wavelengths and frequencies that humans can see • All the colors of the rainbow as well as white light • White light is all the rainbow colors combined • Certain visible light frequencies are required for good health

11. Ultraviolet • Higher frequency than visible • Blue and purple are the highest frequencies we can see in the visible light spectrum, but we can’t see actual ultraviolet light • Positive and negative affects + Can kill bacteria + Vitamin D: body needs sunlight to manufacture Vit D for calcium absorption • sunburns, skin cancer, eye damage, wrinkles (gasp) and premature aging of the skin • UV can travel through clouds

12. X-Rays • Even shorter wavelength • Carry a great deal of energy!!!!! • Easily penetrate a variety of substances • Useful in medical fields for looking at bones, and dense tissue • Can be harmful to living cells – amount of x-rays need to be limited. Professionals wear lead aprons

13. Gamma Rays • Shortest wavelength • Carry the most energy • Exposure to small amounts happens all the time, but not too dangerous if the minimum amount exposure • Can be used to treat some forms of cancer • Treatment: light rays focused on tumors in the body (can kill healthy cells, as well, though, so some risk is involved)

15. Interactions of Light Waves • Reflection – mirror, sunlight • Refraction – prism, lenses, magnifying glasses • Diffraction – squinting your eyes, edges of shadows blurry • Interference – constructive and destructive

16. Light and Color • Visible Light is composed of many colors Purple has the highest frequency and red has the lowest frequency

17. Mixing Colors of Light(Different from mixing colors of pigment) • In order to get white light, combine all colors of light, or simply add just blue, green and red. • This is called color addition

18. Mixing Colors of Pigment(Different from mixing colors of light) • Mixing pigments is like mixing paint • Pigments absorb certain colors of light and reflect others • Red absorbs all colors but reflects red, that is why we see red • Color subtraction