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Chapter 7

Chapter 7. OPTICS & WAVE EFFECTS Dr. Babar Ali. CHAPTER OUTLINE. REFLECTION. When waves encounter a barrier, they bounce back and some reflection occurs

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Chapter 7

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  1. Chapter 7 OPTICS & WAVE EFFECTS Dr. Babar Ali

  2. CHAPTER OUTLINE

  3. REFLECTION • When waves encounter a barrier, they bounce back and some reflection occurs • Echo is reflection of sound waves! • The Law of Reflection states that the angle of incidence is equal to the angle of reflection

  4. REFRACTION • In a transparent medium, some light is reflected and some transmitted • Transmitted light changes speed and direction  ‘bends’ • Bending of light due to a D in speed is called refraction

  5. INDEX OF REFRACTION • The ratio of the speed of light in the two media is defined as the index of refraction Velocity of light in vacuum Index of refraction = Velocity of light in medium 3.0 x 108 m/s • Since the speed of light is greatest in vacuum, the index of refraction (n) is always > 1

  6. Example 1: Ice has an index of refraction of 1.305. What is the velocity of light in ice? n = 1.305 c = 3.0x108 m/s v = ??? v = 2.3 x 108 m/s

  7. Example 2: Water has an index of refraction of 1.33. What is the speed of light in water? n = 1.33 c = 3.0x108 m/s v = ??? v = 2.26 x 108 m/s

  8. Example 3: The speed of light in glass is 2.0 x 108 m/s. What is the index of refraction of glass? n = ??? c = 3.0x108 m/s v = 2.0x108 m/s n = 1.5

  9. Example 4: Material A has an index of refraction of 2 and material B has an index of refraction of 3. In which material does light travel faster? Constant As n increases v decreases Light travels faster in A than B

  10. DISPERSION • When white light passes through a glass prism it is dispersed into a spectrum of colors • Each wavelength (λ) of visible light refracts differently • The longest λ (red) refracts the least; shortest λ (violet) refract the most

  11. DIFFRACTION • Bending of waves around obstacles is called diffraction • Waves passing through 1 or 2 slits near one another create a unique pattern due to diffraction. (Animations 1 and 2) • Ex. Sound can be heard around corners, and light can be seen through openings due to diffraction

  12. INTERFERENCE • When two waves occupy the same space, interference occurs • Constructive interference when waves are in phase they add crests and troughs align Larger amplitude • As a result, reinforcement of the waves occurs

  13. INTERFERENCE • Destructive interference occurs when the waves are out of phase, subtracting crests and troughs aligned opposite of each other • As a result, cancellation of the waves occurs

  14. POLARIZATION • Refraction and interference are evidence that light is wavelike in nature • Polarization of light is evidence that light is a transverse wave • A transverse wave can be generatedalong different planes. Such wave is called un-polarized. Un-polarized

  15. POLARIZATION • When un-polarized light passes through a Polarizer, only the waves in the direction of the filter can pass through. Un-polarized light Pass through filter Blocked by filter Polarized light

  16. POLARIZATION • When two polarizing filters are used, the light transmitted through depends on their alignment Blocked by filter Blocked by filter No light passes through

  17. SIMPLE LENSES • A practical effect of refraction occurs in lenses. • There are two types of lenses: CONVEX CONCAVE

  18. PROPERTIESOF LENSES Focal Point F

  19. PROPERTIESOF LENSES Focal Point F

  20. VISION CORRECTION • Nearsightedness occurs when image is formed in front of the retina. • This condition is corrected by wearing glasses with diverging (concave) lenses.

  21. VISION CORRECTION • Farsightedness occurs when image is formed behind the retina. • This condition is corrected by wearing glasses with converging (concave) lenses.

  22. COLOR • Colors of most objects are due to selective reflection and absorption of light by a material • The red glass appears red because it reflects the red component present in white light, and absorbs all other colors

  23. COLOR • When light rays are reflected from the top and bottom surfaces of a thin film (i.e., soap bubble, oil film, etc.), constructive and destructive interference occurs and colorful pattern appear

  24. THE END

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