Light, Optics, and Electromagnetic Waves in Physics

1. Describe what a lens and a mirror do to light rays. S-97

2. Draw a diagram that shows how light travels from an object to a mirror, then to your eyes. S-99

3. Light and Optics

4. 8.1 Maxwell’s Equation

5. After the work of Oerseted, Ampere and Faraday James Clark Maxwell – all electric and magnetic phenomena can be described by four equations Fundamental – even taking into account relativity Require Calculus 8.1 Maxwell’s Equation

6. Gauss’s Law – relates electric field to electric charge • Magnetic field Law – • Faraday’s Law – electric field is produced by magnetic field • Ampere’s Law – magnetic field produced by an electric current, or changing electric field 8.1 Maxwell’s Equation

7. 8.2 Production of Electromagnetic Waves

8. How Electromagnetic Waves are Produced The charged particle oscillate As it travels one direction a current is produced This generates a magnetic field When the direction changes, so does the current and the magnetic field EMR Production 8.2 Production of Electromagnetic Waves

9. Electric and magnetic fields are perpendicular to each other The fields alternate in direction These are electromagnetic waves Transverse In general – accelerating electric charges give rise to electromagnetic waves 8.2 Production of Electromagnetic Waves

10. 8.3 Electromagnetic Spectrum

11. Electromagnetic Spectrum 8.3 Electromagnetic Spectrum

12. All EMR has a velocity of in a Vacuum Velocity decreases with increase in optical density The wave equation becomes Unlike Sound – energy depends on frequency h – Planck’s Constant 8.3 Electromagnetic Spectrum

13. 8.4 The Ray Model of Light

14. Light travels in a straight line in most cases (away from very large gravitational fields) Ray Model – Light travels in straight line pathways called rays represents a narrow beam of light 8.4 The Ray Model of Light

15. We see an object when rays of light come from the object to our eyes 8.4 The Ray Model of Light

16. 8.5 Reflection

17. When light strikes an object it is Reflected – bounces off Refracted – transmitted through Absorbed – converted to a different form of energy Law of Reflection 8.5 Reflection

18. Diffuse Reflection – on a rough surface Rays don’t form an pattern We see color Specular Reflection – smooth surface Patterns form images 8.5 Reflection

19. What is the speed of light in a vacuum? • If the wavelength of light is 512 nm, what is the frequency? • What would be the energy in a photon of that frequency? S-100

20. How are images formed Your eye sees the intersection of rays from an object 8.5 Reflection Applet

21. Object Distance – from mirror to the object Image Distance – from mirror to the image Virtual Image – imaginary intersection of light rays Real Image – actual intersection of light 8.5 Reflection

22. A man stands in front of a mirror. He is 1.8 m tall. What is the minimum height the mirror must be for him to see his entire image? S-101

23. 8.6 Formation of Images by Spherical Mirrors

24. Spherical Mirrors – form a section of a sphere Convex – reflection on outer surface of sphere Concave – reflection on inner surface of sphere 8.6 Formation of Images by Spherical Mirrors 23.3

25. Terms Principal Axis – straight line normal to the center of the curve Focus – point where parallel rays intersect Vertex – center of the mirror Focal Length – distance from vertex to focus Images from distant objects are produced at the focal point 8.6 Formation of Images by Spherical Mirrors

26. The focal point is actually an approximation The greater the curve of a mirror, the worse is the approximation Called Spherical Aberration Examples of Visual Aberrations 8.6 Formation of Images by Spherical Mirrors

27. All rays follow the law of • reflection • Two Rules • A ray parallel to the principle axis reflects through the focal point • A ray through the focal point reflects parallel • Examples of Diagrams – Concave Mirrors • Real Images • Virtual Image 8.6 Formation of Images by Spherical Mirrors

28. Convex Mirrors only form virtual images • Rules • Rays parallel to the principle axis reflect away from the focal point • Rays headed for the focal point reflect parallel 8.6 Formation of Images by Spherical Mirrors

29. Sketch the image formed by a 2.00 m tall dog standing 4.00 m from a convex mirror with a focal length of 1.50 m. S-102

30. Curved Mirror Equations ho-object height hi-image height do-object distance di-image distance The Mirror Equation Magnification 8.6 Formation of Images by Spherical Mirrors

31. Sign Conventions Image Height + upright (virtual) - inverted (real) Image and Object Distance + front of mirror - behind mirror Magnification + upright image - inverted image 8.6 Formation of Images by Spherical Mirrors

32. Sign Conventions Focal Length + concave mirror - convex mirror 8.6 Formation of Images by Spherical Mirrors

33. 8.7 Index of Refraction

34. Index of Refraction – the ratio of the speed of light in a vacuum to the speed in a given material 8.7 Index of Refraction

35. Value can never be less than 1 8.7 Index of Refraction

36. 8.8 Refraction: Snell’s Law

37. Refraction – when a ray of light changes direction as it changes media The change in angle depends on the change in velocity of light (or the index of refraction of the two media) 8.8 Refraction: Snell’s Law

38. Snell’s Law – relates the index of refractions and the angles Also called the Law of Refraction If light speeds up, rays bend away from the normal If light slows down, rays bend toward the normal 8.8 Refraction: Snell’s Law

39. Refraction occurs when one side of the wave slows down before the other 8.8 Refraction: Snell’s Law

40. 8.9 Total Internal Reflection; Fiber Optics

41. When light travels into a less optically dense medium, the ray bends away from the normal As the angle increases, the angle of refraction eventually reaches 90o. This is called the critical angle 8.9 Total Internal Reflection; Fiber Optics

42. Above the critical angle, light reflects following the law of reflection Used in fiber optics 8.9 Total Internal Reflection; Fiber Optics

43. A frog stands 12 cm in front of a concave mirror with a focal length of 15 cm. The frog is 9 cm tall. • What is the distance and height of the image? • What would be the distance and height of the image if the mirror was convex? S-103

44. 8.10 Thin Lenses; Ray Tracing

45. Thin lens – very thin compared to its diameter Diagrams are similar to mirrors Converging – rays converge 8.10 Thin Lenses; Ray Tracing

46. Converging Lenses • A ray parallel to the Principle Axis refracts through F • A ray through F’ refracts parallel. • A ray through the optical center, O, does not refract 8.10 Thin Lenses; Ray Tracing Converging Lens

47. SOLAR COOKING On a Balmy Winters Day! S-104

48. A diverging lens with a focal length of 18 cm is used to produce the image of a rather cute rodent that is 1.3 cm tall. The rodant stands 22 cm from the lens. • What is the distance, height, and magnification of the image? • What would it be if the lens was converging. S-105

49. A converging lens produces an image of an stinky fruit 17 cm from the lens. The object was originally placed 12 cm from the lens, and the image is projectable. A. What is the focal length of the lens? B. What is the magnification of the image? S-106

50. A diverging lens produces an image of an cat with a bad haircut 17 cm from the lens. The object was originally placed 12 cm from the lens. A. What is the focal length of the lens? B. What is the magnification of the image? S-107