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23.2 Refraction

23.2 Refraction. pp. 503 – 506, and 525 (24.1) Mr. Richter. Agenda. Warm-Up Notes: The Speed of Light Index of Refraction Angle of Refraction Total Internal Reflection Dispersion . Objectives: We Will Be Able To…. Calculate the wavelength and frequency of light.

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23.2 Refraction

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  1. 23.2 Refraction pp. 503 – 506, and 525 (24.1) Mr. Richter

  2. Agenda • Warm-Up • Notes: • The Speed of Light • Index of Refraction • Angle of Refraction • Total Internal Reflection • Dispersion

  3. Objectives: We Will Be Able To… • Calculate the wavelength and frequency of light. • Describe what happens when light goes from one material to another. • Understand the index of refraction. • Explain total internal reflection and dispersion.

  4. Warm-Up: • When a pencil is partially submerged, it looks like it bends at the surface of the water. • What is really happening?

  5. The Speed of Light

  6. The Speed of Light • Reminder: all light travels at the speed of light • 300,000,000 m/s. Always. • The relationship between the speed of light, frequency and wavelength is the same as it is for all other waves.

  7. The Speed of Light: Your Turn • The broadcast frequency of Jammin’ 94.5 is 94,500,000 Hz. What is the wavelength of the waves sent from the radio tower? • λ= 3.17 m

  8. Index of Refraction

  9. Index of Refraction • Light bends when it passes into a different medium. • It appears to slow down. BUT IT DOESN’T! LIGHT TRAVELS AT THE SPEED OF LIGHT. • So what happens? • Different materials have different molecular structures. Some materials take longer to absorb and re-emit light.

  10. Index of Refraction • Every transparent material has an index of refraction. • The index of refraction (n) of a material indicates how slowly light appears to move in that material. • The index of refraction measures how much light bends.

  11. Index of Refraction • The higher the index of refraction: • The slower light appears to move. • The more light bends.

  12. Angle of Refraction Which way does light bend?

  13. Angle of Refraction • Imagine your right arm as a wave. • As you walk, your arm moves with you through the air. • However, if you drag your hand along a fence, your arm drags behind, bending your body.

  14. Angle of Refraction • The same thing happens with waves of light. • As waves encounter a new material, they will slow down (or speed up), bending the wave.

  15. Angle of Refraction: Which Way Does Light Bend? • If light travels from a high index of refraction to a low index of refraction, light bends away from the normal line. • Example: glass to air. • If light travels from a low index of refraction to a high index of refraction, light bends toward the normal line. • Example: air to glass.

  16. Angle of Refraction: Which Way Does Light Bend?

  17. Total Internal Reflection

  18. Total Internal Reflection • Total internal reflection occurs when the angle of refraction is greater than 90°. • This only occurs when light travels from a medium with a higher index of refraction to a lower index of refraction. • Water to air, for example.

  19. Total Internal Reflection • When traveling from high n to low n, there is a critical angle where light refracts at exactly 90°. • When light travels from water to air, the critical angle is around 49°. • At angles greater than 49° the light is reflected, not refracted.

  20. Fiber Optics • Fiber optic cables are thin, bendable pieces of glass wound together. • The glass allows total internal reflection of light over long distances, with very little loss of light. • Allows a very quick transfer of information with very little loss of clarity.

  21. Dispersion

  22. Dispersion • The index of refraction depends on the wavelength of light. • Or in other words: Light bends differently depending on its wavelength, • and by extension, its color. • This is how prisms separate light. • Blue light has a shorter wavelength than red, so it bends at a greater angle of refraction.

  23. Rainbows • Dispersion is most easily observed in nature as rainbows. • Water droplets act as prisms and disperse components white light at different angles.

  24. Wrap-Up: Did we meet our objectives? • Calculate the wavelength and frequency of light. • Describe what happens when light goes from one material to another. • Understand the index of refraction. • Explain total internal reflection and dispersion.

  25. Homework • Due Thursday: • p. 518 Reviewing Concepts #11, 12, 14, 15 • p. 519 #5, 6

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