Electromagnetic Radiation … aka Light

1. Electromagnetic Radiation … aka Light The EM spectrum Not just the “light” we can see… Ranges from low frequency radio waves to high frequency x-rays Small window of frequencies called “visible light”

2. Light Properties: Review • Electromagnetic radiation travels ________________in a vacuum • or about 186,000miles/second • This velocity has a symbol of? • Travels in rays… straight line from an origin. 3.00 E8 m/s c

3. Visible Light • A small slice of the EM spectrum can be detected by human eyes. • Color is the brains code for the frequency of perceived light. • Roy G. Biv – acronym • On the left are low frequencies and long wavelengths. On the right are high frequencies and short wavelengths R O Y G B I V

4. Color # 1- Rules for Color • White is ALL colors of the VS (visible spectrum)

5. Color # 1- Rules for Color • Black is the absence of all colors. • Black appears black because nothing is reflected from it… therefore the light energy is turned to heat!

6. Color # 1- Rules for Color • Objects of a particular color absorb all other colors except for the color they “normally” appear. • Ex. Green plants absorb all colors (roybiv) and use these energy frequencies to produce sugar during photosynthesis…, except green… they reflect green.

7. Color # 2- Rules for Color • An object’s color depends SOLELY on the color of light that is reflected off of it. Green only is reflected White light (roygbiv) Object looks green

8. Color # 3- Rules for Color • An object’s color depends SOLELY on the color of light that is reflected off of it. Filtered red light No light is reflected, no light reaches the eye, so object appears black! The turtle absorbed red light

9. Velocity of light through other materials – Snell’s Law • When light travels through substances, its velocity is effected. • The amount the speed is reduced is the optical density (n) • n = c / velocity in the substance

10. Find the v of each of these. n = c/v

11. Law of Reflection • Establish “normal” – an imaginary perpendicular line to the surface of a reflective object. normal Θ Θ = i r Angle of incidence Angle of reflection mirror

12. Inverted images • Mirrors produce images which have an “apparent distance” equal to that of the real object is from the mirror. • Images are also “inverted” • Mirrors need not be the same size as the object to produce a full sized image. d d

13. Mirrors and Reflection • Light rays travel in parallel rays from a source to an object that reflects them. • A reflection can be “diffuse”, “perfect”, or “focused” • Mirrors create either perfect (specular) or focused reflections depending on their shape.

14. Diffuse Reflection • The rays are scattered in different directions. This is the way we see most objects in everyday life.

15. Perfect (specular) reflection • Plane mirrors create perfect parallel reflection of rays. mirror

16. Focused reflection • Concave and Convex Mirrors create focused reflections. They still obey the Law of Reflection. • Convex Concave Focal point

17. Mirrors and Reflection #4 enlarged Multiple normals, resulting in slightly different reflected angles

18. Refraction • High frequencies are more affected by this phenomenon. • Snell’s Law also predicts how much it will be bent in the equation… ni sinΘi =nrsinΘr • n = optical density or Index of refraction.

19. Refraction#1 When light changes the material in which it travels, changes in velocity cause a change in direction. The θincidence is different than the θrefracted.

20. Refraction#2 Optical density low Optical density high Optical density low Optical density of the material determines amount of “bending” parallel High O.D. = small Θ Low O.D. = larger Θ

21. air water Virtual fish Actual fish

22. Lenses • Lenses obey Snell’s Law by refracting light to a certain degree. • Lens shape has the biggest effect on light behavior. • Two types : Concave Convex

23. Renaissance Masters - Tracers???