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REFLECTION & REFRACTION

REFLECTION & REFRACTION. Physics. Light at Boundaries. When light reaches a new material, two things happen: Some light bounces back . This is called reflection. Some light enters (goes through) but turns this is called refraction. Vocabulary.

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REFLECTION & REFRACTION

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  1. REFLECTION & REFRACTION Physics

  2. Light at Boundaries • When light reaches a new material, two things happen: • Some light bounces back. This is called reflection. • Some light enters (goes through) but turns this is called refraction.

  3. Vocabulary • Incident wave = the wave that is coming in • Reflected wave = the wave that bounces back • Transmitted wave / Refracted wave = the wave that makes it through

  4. How do we measure angles? Step 1: Draw the normal line (perpendicular to the surface). Step 2: Measure all angles from the Normal.

  5. Why do some materials reflect images and others do not?

  6. We always measure angles from the NORMAL line!!! • Draw a dotted line that is PERPENDICULAR to the surface. That is called the NORMAL line. All angles are measured from this line. θ θ θ

  7. LAW OF REFLECTION • Incident Angle = Reflected Angle • θ1 = θ2 • Remember to measure from the normal line. θ1 θ1 θ2 θ2 θ2 θ1

  8. PRACTICE: Use similar triangles. • A laser is being held 10 cm above a flat mirror and 25 centimeters in front of it. Meanwhile, the wall is 5 meters away. Where should we place a bull’s eye on the wall in order to catch the laser dot?

  9. SOLUTION 10 cm X θ1 θ2 25 cm 5 meters We know both triangles have the same angles. So we can use ratios. 10 = X cross multiply 50 = 25X X = 2 meters high 25 5 If we wanted to solve for the angles involved we could use ARC TANGENT. Remember that the incident angle is measured from the normal line!! In this case the bottom red triangle angle = arctan(10/25) = 22 degrees This means that the incident angle = 90 – 22 = 68 degrees

  10. How does a mirror work?Your brain assumes light goes straight.

  11. Miku – World Is Mine • https://www.youtube.com/watch?v=O17f3lB7BFY

  12. Is light the only wave that reflects? • No. Sound reflections are called echoes. • (Any wave can reflect.)

  13. Marching Band Analogy

  14. Now let’s try an angled march.

  15. Things to Notice • The line always turns TOWARDS the slow guy. • When the wave eventually comes back out it is at the same angle it started.

  16. Index of Refraction = n Definition: • Tells you how hard it is for light to get through a material • If n = 1 there is no resistance at all. It is as easy as outer space. (air = 1) • If n = 2 then it is twice as hard to get through as outer space. (diamond = 2.4)

  17. To calculate the index. • Divide the regular speed of light (300 million) by the speed of light in the new material. Equation: • n = speed of light in space speed of light in new material n = c v

  18. PRACTICE • Light only moves 226 million m/s in water. What is the index of refraction?

  19. Practice • Silicon has an index of 3.96. How fast does light move in silicon?

  20. Predicting Refraction • When light goes from a low index (easy) into a high index (hard) then the wave will turn TOWARDS the normal line. Example is light from my flashlight entering the water. Index of air = 1 Index of water = 1.33 Fish thinks you are a giant!!

  21. Predicting Refraction • When light goes from a high index (hard) into a low index (easy) then the wave will turn AWAY FROM the normal line. Example is light reflecting off a fish and out of the water. You think the fish is really far away. Index of air = 1 Index of water = 1.33

  22. Physics Sound

  23. Sound Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • Sound is a longitudinal wave that requires a medium. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Draw this way: Vibrating Object Compression: High pressure Rarefaction: Low Pressure

  24. Volume • Depends on the amplitude of a wave. • Means – How high is the pressure in the high pressure zone? • Measure it using the decibel scale

  25. Pitch • Depends on the frequency or wavelength. • Means – How many pressure zones hit my ear each second? Example: • 265 Hz is 265 vibrations per second giving us middle C. • High pitched – rapid vibration (Sopranos) • Low pitched – slow vibration (Bass)

  26. Speed of Sound: • The speed of sound is: 343 m/s

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