Optical Phenomenal

1. Optical Phenomenal Chapter 14 section 3

2. Objectives • Predict whether light will be refracted or undergo total internal reflection. • Recognize atmospheric conditions that cause refraction. • Explain dispersion and phenomena such as rainbows in terms of the relationship between the index of refraction and the wavelength.

3. Total Internal Reflection • Total internal reflection can occur when light moves along a path from a medium with a higher index of refraction to one with a lower index of refraction. • At the critical angle, refracted light makes an angle of 90º with the normal. • Above the critical angle, total internal reflection occurs and light is completely reflected within

4. Critical Angle • Snell’s law can be used to find the critical angle. • Total internal reflection occurs only if the index of refraction of the first medium is greater than the index of refraction of the second medium.

5. Example • Find the critical angle for a water-air boundary if the index of refraction of water is 1.333

6. Atmospheric Refraction • Refracted light can create a mirage. • What is a mirage? • A mirage is an optical effect of the atmosphere caused by refraction when light passes from air with one density into air with a different density and the object appears displaced from its true position. • The mirage called an inferior mirage occurs when the image appears below the true location of the observed object. • During a phenomenon called looming, objects sometimes appear to be suspended above the horizon. • Looming is considered a superior mirage because the image is seen above its true position. • A mirage that changes the apparent size of an object is called towering. • A type of towering, called Fata Morgana, is frequently observed in coastal areas as towering castles that appear out of thin air.

7. Mirages • A mirage is produced by the bending of light rays in the atmosphere where there are large temperature differences between the ground and the air.

8. Mirages

9. Dispersion • Dispersion is the process of separating polychromatic light into its component wavelengths. • White light passed through a prism produces a visible spectrum through dispersion.

10. Rainbows • Perhaps the most spectacular and best known atmospheric optical phenomenon is the rainbow. • Sunlight and water droplets are necessary for the formation of a rainbow. • Furthermore, the observer must be between the Sun and rain. • When a rainbow forms, the water droplets act as prisms and refraction disperses the sunlight into the spectrum of colors, a process called dispersion. • The curved shape of the rainbow results because the rainbow rays always travel toward the observer at an angle between 40 and 42° from the path of the sunlight.

11. Rainbows

12. Lens Aberration • Chromatic aberration is the focusing of different colors of light at different distances behind a lens. • Chromatic aberration occurs because the index of refraction varies for different wavelengths of light.

13. Lens aberration

14. Video • Watch a video

15. Go over lab • Lets go over lab

16. Homework • Do problems 1-4 pg .502

17. Closure Today we learned about optical phenomena Next class we are going to have a lab