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Chapter 14

Chapter 14. Characteristics of Light. Section 14.1. Electromagnetic Waves. Light is made of electromagnetic waves. Take a prism and break up white light into a rainbow like band of colors. These are all in the visible spectrum. Red, orange, yellow, green, blue, indigo and violet.

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Chapter 14

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  1. Chapter 14

  2. Characteristics of Light Section 14.1

  3. Electromagnetic Waves • Light is made of electromagnetic waves. • Take a prism and break up white light into a rainbow like band of colors. These are all in the visible spectrum. • Red, orange, yellow, green, blue, indigo and violet. • ROYGBIV

  4. Electromagnetic Waves • The spectrum also includes non-visible electromagnetic waves, such as x-rays, microwaves, radio waves, and radiation. • Because they all are electromagnetic waves they all have similar properties.

  5. Electromagnetic Waves • Electromagnetic waves are transverse waves consisting of oscillating electric and magnetic fields at right angles to each other. • Oscillate: to have a periodic vibration

  6. Electromagnetic Waves • Electromagnetic waves vary depending on frequency and wavelength • All electromagnetic waves move at the speed of light

  7. Electromagnetic Waves • We will use 3.00 X 108 m/s as the speed of light, c. • The wave speed equation is: • c = f • Speed of light = frequency X wavelength

  8. Sample Problem • The AM radio band extends from 5.4 X 105 Hz to 1.7 X 106 Hz. What are the longest and shortest wavelengths in this frequency range? • f1 = 5.4 x 105 Hz f2 = 1.7 x 106 Hz • c = 3.0 x 108 m/s • c = f • = c/ f • 1 = 5.6 x 102 m • 2 = 1.8 x 102m

  9. Laser Light travels in straight lines. • Light travels in straight lines. • Show the laser on the wall. Put an index card in the beam. This shows that the light is traveling in a straight line, but you can only see it when it hits something. • Put some chalk dust in the beam to show it is continuous. • Brightness decreases by the square of the distance form the source • Show how the size of the dot the laser makes gets bigger as it gets further from the source.

  10. The brightness of light is inversely proportional to the square of the distance from the light source. • Ex. If you move twice as far away from the light source, ¼ as much light falls on the book.

  11. Flat mirrors Section 14.2

  12. Reflection of Light • Reflection – the turning back of an electromagnetic wave at the surface of a substance

  13. Clear vs. Diffuse Reflection • Specular reflection: light reflected from smooth shiny surfaces • In specular reflection the incoming and reflected angles are equal (=’) • Diffuse reflection: light is reflected from a rough textured surface

  14. Diffuse Reflection: Definition, Examples and Surfaces • http://education-portal.com/academy/lesson/diffuse-reflection-definition-examples-surfaces.html#lesson

  15. Part 2 - Reflection • Normal • Reflection from a mirror: • Reflected ray • Incident ray • Angle of reflection • Angle of incidence • Mirror

  16. Reflection of Light • Angle of incidence – the angle between a ray that strikes a surface and the normal to that surface at the point of contact. • Angle of reflection – the angle formed by the line normal to a surface and the direction in which a reflected ray moves • Normal is a line perpendicular to the reflection surface.

  17. Angle of incidence = Angle of reflection • The Law of Reflection • In other words, light gets reflected from a surface at THE SAME ANGLE it hits it. • The same !!!

  18. Reflection: Angle of Incidence and Curved Surfaces • http://education-portal.com/academy/lesson/reflection-definition-angles-of-incidence-diffuse-reflection.html#lesson

  19. Drawing a Reflected Image • Use ray diagrams to show image location • We will find the virtual image (the image formed by light rays that only appear to intersect)

  20. Drawing a Reflected Image • Draw the object in front of the mirror • Draw a ray perpendicular to the mirror’s surface. Because this is 0 from normal, the angle is the same from the mirror to the virtual object • Draw a second ray that is not perpendicular to the mirror’s surface from the same point to the surface of the mirror. • Next, trace both reflected rays back to the point from which they appear to have originated, that is, behind the mirror. Use dotted lines when drawing lines that that appear to emerge from behind the mirror. The point at which the dotted lines meet is the image point.

  21. Flat Mirrors • Image is VIRTUAL, UPRIGHT, UNMAGNIFIED

  22. Chapter 14 14.3 Concave Mirrors

  23. Spherical Mirrors • A spherical mirror has the shape of part of a sphere’s surface. The images formed are different than those of flat mirrors. • Concave mirrors were silvered on the inside of the sphere and convex mirrors were silvered on the outside of the sphere. 

  24. Concave Spherical Mirror • An inwardly curved, mirrored surface that is a portion of a sphere and that converges incoming light rays.

  25. Concave Spherical Mirrors

  26. Principle axis - the line passing through the center of the sphere and attaching to the mirror in the exact center of the mirror • Center of curvature - the point in the center of the sphere from which the mirror was sliced  (C) • Vertex - the point on the mirror's surface where the principal axis meets the mirror (A)

  27. Focal point - midway between the vertex and the center of curvature (F) • Radius of curvature - the distance from the vertex to the center of curvature (R) • Focal length - the distance from the mirror to the focal point, one-half the radius of curvature (f)  • http://www.youtube.com/watch?v=np8lENrge0Q • http://www.youtube.com/watch?v=jrje73EyKag

  28. The light bulb is distance p away from the center of the curvature, C. Light rays leave the light bulb, reflect from the mirror and converge at distance q in front of the mirror. Because the reflected light rays pass through the image point, the image forms in front of the mirror. Concave Spherical Mirrors

  29. Concave Spherical Mirrors • If you were to place a sheet of paper at the image point, you would see a clear, focused image of the light bulb (a real image). If the paper was placed in front of or behind the image point, the image would be unfocused.

  30. Concave Spherical Mirrors • Real image – an image formed when rays of light actually intersect at a single point • Focal length – equal to half the radius of curvature of the mirror.

  31. Concave Spherical Mirrors • Mirror equation: 1/p + 1/q = 2/R • 1 + 1 = 2 . • Object distance Image distance radius of curvature • Or: 1/p + 1/q = 1/f • 1 + 1 = 1 . • Object distance Image distance focal length

  32. Concave Spherical Mirrors • Object and image distances have a positive sign when measured from the center of the mirror to any point on the mirror’s front side. • Distances for images that form on the backside of the mirror always have a negative sign.

  33. Concave Spherical Mirrors • The measure of how large or small the image is with respect to the original object is called the magnification of the image. • M = h’/h = -(q/p) • Magnification = image height = image distance • object height object distance

  34. Concave Spherical Mirrors • For spherical mirrors, three reference rays are used to find the image point. The intersection of any two rays locates the image. The third ray should intersect at the same point and can be used to check the diagram.

  35. Rules for drawing reference rays

  36. Ray 1

  37. Ray 2

  38. Ray 3

  39. All three rays together

  40. Spherical Mirrors - Concave • Image is REAL, INVERTED, and DEMAGNIFIED !!! • C • F

  41. Concave Spherical Mirror • When an object changes its location in relation to the mirror, its image changes in location, and form.

  42. Concave Spherical Mirror

  43. Distance greater than focal length

  44. Distance = focal length

  45. Between focal length and mirror

  46. Spherical Mirrors – ConcaveObject Inside the Focal Point • Image is VIRTUAL, UPRIGHT, and MAGNIFIED • F • C

  47. Concave Spherical Mirrors

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