The Electromagnetic Spectrum and Col or Pe rc ep ti on

1. The Electromagnetic Spectrum andColorPerception

2. What do we know so far about electromagnetic waves? • Electromagnetic waves (EM waves) carry energy. • EM waves can travel through empty space OR matter. • ALL EM waves are transverse waves.

3. What more is there to know about EM waves? • EM waves have a wide range of wavelengths/frequencies. • Each wavelength/frequency of EM waves is a different type of energy. • gamma rays • X-rays • ultraviolet radiation • visible light • infrared radiation • microwaves • television/radio waves

5. Most of the EM energy that makes it to the surface of Earth is in the middle range of the electromagnetic spectrum: • ultraviolet radiation • visible light • infrared radiation

6. What is ultraviolet radiation? • Ultraviolet radiationis the range of EM waves with frequencies higher than violet on the visible spectrum. (ULTRA-violet) • They have shorter wavelengths, which means higher frequencies-so because of this we know they have more energy than visible light.

7. Because of the high energy of ultraviolet radiation, too much exposure is damaging to the eyes and skin. • This is why sunblock is important. • This is why sunglasses are important.

8. What is visible light? • Visible light is the range of EM waves that can be detected by the human eye. • The entire range of visible light is called the visible light spectrum.

11. Violet (highest frequencies/shortest wavelengths/highest energy) • Indigo • Blue • Green (middle frequencies/middle wavelengths/middle energy) • Yellow • Orange • Red (lowest frequencies/longest wavelengths/lowest energy)

12. ROYG. BIV

13. The visible light spectrum is the middle range of wavelengths/frequencies of EM spectrum. • The longer the wavelength, the lower the energy; the shorter the wavelength, the higher the energy. • Red has lowest energy; violet has the highest energy.

14. Why do we see color based on the visible light spectrum? • The human eye reacts to different energies and frequencies of light so that different colors are seen. • Higher frequencies (shorter wavelengths) are perceived as colors toward the blue-violet range and have higher energy. • Lower frequencies (longer wavelengths) are perceived as colors toward the orange-red range and have lower energy.

15. The reason we see “stuff” in color: • Most materials absorb light of some frequencies and reflect the rest. • If a material absorbs a certain frequency of light, that frequency will not be reflected, so its color will not be perceived by the observer. • If the material does not absorb a certain frequency of light, that frequency will be reflected, so its color will be perceived by the observer.

16. If all colors of light are reflected by a material, it will appear white. If all colors of light are absorbed by a material, it will appear black.

17. The color that we see depends on (1) the color of light that is shined on the object and (2) the color of light that is reflected by the object. For example, if an object reflects red wavelengths and absorbs all others, the object will appear red in color.

18. Color filters allow only certain colors of light to pass/transmit through them; they absorb or reflect all other colors. • For example, a blue filter only transmits blue light. • Objects seen through a blue filter will look blue if the objects reflect blue. • Objects of other colors will appear black because the other color wavelengths are being absorbed by the filter.

19. What is infrared radiation? • Infrared radiation is the range of electromagnetic waves with frequencies lower than red on the visible spectrum, thereby having longer wavelengths and less energy than red wavelengths.

20. All objects emit infrared radiation, and hotter objects emit more infrared radiation than cooler objects. • Heat energy is transmitted by infrared radiation. • When objects absorb infrared radiation, they become warmer.