Tyler Junior College Physics 1405 Elementary Physics

1. Tyler Junior CollegePhysics 1405Elementary Physics Section Cuatro Light & Radiation

2. Tyler Junior CollegePhysics 1405Elementary Physics Chapter 26 Properties of Light

3. Important Concept • Electromagnetic Waves • Weirdness of Light • EM spectrum • Opacity in general • Opacity of atmosphere

4. Electromagnetic Waves • EM Waves are LIGHT! • Sometimes light is called EM radiation. • Light is generated whenever a charged object accelerates.

5. Self-PropagatingElectric & Magnetic Fields • The E and M waves are “in phase”.

6. Weirdness of Light • You can’t see light, only its effects! • Light behaves as a wave (at times). • Interference, refraction, reflection, λ, f, etc. • Light behaves as a particle (at times). • Discrete packet, photon, momentum, energy, etc. • Light speed is c = 3x108 m/s (in vacuum). • Light travels with the same speed, regardless of reference frame.

7. Different Kinds of Light • What we perceive as color is really different wavelengths of light. • Red light, λ = 700nm • Violet light, λ = 400nm • All colors of light have λ in this range. • This is the range of visible light. • But there is more light outside this range.

8. Electromagnetic Spectrum Long λ Short λ Low f, E High f, E

9. Opacity & Transparency • Opacity – the ability of a material to block radiation; opposite of transparency. • Transparency – the ability of a material to transmit radiation; opposite of opacity. • An opaque object has a large opacity. • A transparent object has a low opacity.

10. Opacity is λ dependent • Whether an object is considered opaque or transparent depends upon the type of radiation. • Example: • Human tissue has high opacity to visible light. • Human tissue has low opacity to x-ray light. • Glass blocks UV & IR but not visible.

11. Opacity Demonstrated

12. Opacity of Earth’s Atmosphere

13. Tyler Junior CollegePhysics 1405Elementary Physics Chapter 27 Color

14. Important Concepts • How the eye perceives color. • Colors are light of different frequency • Mixing colors • Why is the sky blue? • Why is sunset red?

15. How the eye perceives color? • Rods & Cones create color vision. • Rods dominate toward periphery of retina. • Cones dominate in fovea. • There are 3 types of cones: RGB • The optical nerve leaves a blind spot. • The periphery of the retina is very sensitive to motion.

16. Colors are light of different freqs

17. Mixing Colors of Light

18. Additive & Complementary Colors • R, B, G are the additive primary colors • R + B = Magenta • R + G = Yellow • B + G = Cyan • The complement of a color adds to make white. • Magenta + G = white = R+G+B • Yellow + B = white = R+G+B • Cyan + R = white = R+G+B

19. Why Is the Sky Blue?

20. Why is the Sunset Red?

21. Tyler Junior CollegePhysics 1405Elementary Physics Chapter 28 Reflection & Refraction

22. Concepts • Reflection • Refraction • Dispersion • Total Internal Reflection • Lenses • Mirrors

23. REFLECTION

24. Reflection in a plane mirror • Image distance equals object distance. i.e., image appears to be “behind” mirror d d

25. The Law of Reflection Restated • Fermat’s principle of least time: “Out of all the possible paths that light might take to get from one point to another, it takes the path that requires the shortest time” To figure out least time path…

26. Least Time Path = law of reflection observer object mirror image

27. More Plane Mirrors

28. Curved Mirrors • Concave • Convex • Principle axis • Center of curvature • Focal length • Focal point

29. Rules of Curved Mirrors 1. parallel rays reflect through the focal point 2. rays through the focal point reflect parallel 3. rays through the center of curvature reflect back through the center. Drawings to locate images must be drawn to scale to be accurate. A drawing can determine image location, image size, and whether image is inverted.

30. Image Location for Concave Mirror

32. 5 Possible Cases for Object Loc.

33. The 5 Cases

34. Now Convex Mirrors

35. The Rules again… • Parallel rays reflect through the focal point. • Rays through the focal point reflect parallel. …but now the focal point is on the other side of the mirror.

36. Convex Image Location

37. The Convex Cases Objects in mirror are closer than they appear.

38. REFRACTION

39. Refraction Occurs at an Interface

40. Index of Refraction • An indicator of the optical density of a material is the index of refraction.

41. Refraction • When light refracts, the direction of the light ray is changed.

42. Refraction Rules • When light goes from low n to higher n… it refracts toward the normal. • When light goes from high n to lower n… it refracts away from the normal.

43. Refraction Effects • Objects appear closer/larger under water.

44. Refraction Effects • Mirage

45. Dispersion • Not all light is refracted equally. • Violet light is refracted more than red light. • This leads to dispersion of white light through a medium. • Dispersion also explains the rainbow.

46. Dispersion Demonstrated

47. Refraction Effects • Rainbow

48. The Rainbow Explained

49. Tyler Junior CollegePhysics 1405Elementary Physics Chapter 30 Light Quanta

50. Concepts • Blackbody Radiation • Excitation • Emission • Absorption • Spectroscopy • Photoelectric Effect