1. Light and Reflection
Holt Physics

2. 13.1 Characteristics of Light Objectives
I can dentify components of the electromagnetic (EM) spectrum
I can calculate the frequency or wavelength of EM radiation
I can recognize that light has a finite speed
I can state the speed of light in a vacuum
I can describe how the brightness of a light source is affected by distance

3. Electromagnetic Wave Model of Light
Light is a type of electromagnetic radiation
Electromagnetic spectrum includes all EM radiation
EM waves are transverse waves consisting of electrical and magnetic fields oscillating at right angles to each other
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4. Electromagnetic Spectrum
Wavelength (m)
Energy (J) and Frequency (s-1)
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5. Visible Spectrum Wavelength (nm) Energy (J) and Frequency (s-1)
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6. Speed, frequency, and wavelength in EM radiation
EM radiation varies in frequency and wavelength
All EM radiation travels at the same speed
speed of light = 3.00 x 108 m/s in a vacuum
speed varies with the medium
Wave speed equation
c = λν where c = speed of light; ν = frequency; λ = wavelength
v = λf

7. Energy, Frequency, & Wavelength of EMR

8. Photon Model of Light
radiation travels in discrete packets of energy called photons that are continuously emitted from an light source in all directions
energy of these photons is directly proportional to the frequency of the electromagnetic radiation
E = hν; h = Planck’s constant, ν = frequency

9. EM Wave or Photon? Which is Correct?
Strong scientific evidence supports both the particle-like model and wave-like model.
Depending on the problem scientists are trying to solve, either the particle (photon) model or the wave model of radiant energy transfer is used.

10. Wave Fronts
A wave front is the line of particles, perpendicular to the direction of travel, that form the crest

11. Wave Fronts Waves are 3 dimensional
Consist of parallel crests & troughs
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12. Origin of Wave Fronts
As distance increases from source, curvature decreases and approaches a straight line perpendicular to the source.
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13. Wave Fronts and Light Rays
Light waves can be modeled as rays
Ray is a line perpendicular to the wave front
Light rays chart out the path that some spot on the wave front takes over time.

14. Huygen’s Principle
Points along a wavefront generate wavelets that travel forward at the same speed as the wave.
The new wavefront is tangent to the wavelets.
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15. Importance of Huygen’s Principle
Explains how waves propagate
Explains reflection
Explains refraction
Applies to all types of waves
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16. Brightness and Distance
Perception of brightness depends upon how much light falls upon a unit of surface area
light spreads out as it is transmitted,
Therefore, as distance increases, less light falls upon a unit of surface area

17. Illuminance
Luminous flux: the rate at which light is emitted from a source
Illuminance is luminous flux divided by area
So, illuminance decreases with the square of the distance from the source

18. 14.2 Flat Mirrors Objectives
I can distinguish between specular and diffuse reflection of light
I can apply the law of reflection for flat mirrors
I can describe the nature of images formed by flat mirrors

19. Reflection of Light
Light travels in a straight line until it encounters the boundary of a new medium
Reflection: an EM wave (e.g. light) is turned back at a surface
Smoothness of the surface produces different types of reflection:
Diffuse reflection occurs on rough, unpolished surfaces (paper, wood, etc)
Light rays are reflected in many different directions
Specular reflection occurs on smooth, polished surfaces
Light rays are reflected in the same direction

20. Specular and Diffuse Reflection
What do specular and diffuse reflection look like?
Digital Cinematography - shading models

21. Law of Reflection
Angle of incidence = angle of reflection (θi = θr) when measured wrt a line normal to the surface of the mirror.
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22. Wavefronts & Reflection
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23. How do we see images in a mirror?
Images seen on mirrors are formed as:
Light is emitted or reflected off an object
Which is then reflected by the surface of the mirror
Which is then absorbed by our eye
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24. Images Formed in Plane Mirrors
Plane mirrors form virtual images
An image formed by light rays that only appear to intersect (virtual rays)
Image location is determined by constructing ray diagrams

25. Image Formation in Plane Mirror

26. 14.3 Curved Mirrors Objectives
Calculate the distances and focal lengths using the mirror equation for concave and convex spherical mirrors
Draw ray diagrams to find the image distance and magnification for concave and convex spherical mirrors
Distinguish between real and virtual images
Describe how parabolic mirrors differ from spherical mirrors

27. Spherical Mirrors Are the shape of a portion of a sphere
Concave mirrors
Reflect on the inner surface
Form real or virtual images
Convex mirrors
Reflect on the outer surface
Form virtual images

28. Describing a Concave Mirror
Consider a concave mirror as a portion of a slice of a hollow sphere
Principal axis
Center of curvature, C
Vertex, A
Radius of curvature, R
Focal Point, F
Focal length, f

29. Significance of Focal Point
Incident light rays from a distant source can be considered parallel
Light rays from the sun are considered parallel
All incident light rays traveling parallel to the principal axis are reflected through the focal point

30. Law of Reflection Applies Curved Mirrors
With a spherical mirror, the normal to the surface always passes through the center, C
Use the normal to determine the angles of incidence and reflection, just like plane mirrors
θi = θr

31. Images Formed by Concave Mirrors
Size and orientation of image depends upon location of object on the principal axis
May be magnified, reduced, or same size as object
May be inverted or upright
May be real or virtual

32. Predicting Image Location

33. Determining size of image

34. Interpreting the Magnification Equation
Sign conventions for Magnification
Orientation of image
Sign of M
Type of image
Upright +
Virtual
Inverted -
Real

35. Drawing Ray Diagrams for Spherical Mirrors
Rules for Drawing Reference Rays
Ray
Line drawn from object
Line drawn from mirror to image after reflection 1
Parallel to principal axis
Through F 2
Parallel to principle axis 3
Through C
Back through C

36. Concave Spherical Mirrors
C = center
F = focal point
F = ½ Radius

37. Image formation in Concave Mirror

38. Image formation in Concave Mirror

39. Image formation in Concave Mirror

40. 14.4 Color and polarization Objectrives
Recognize how additive colors affect the color of light
Recognize how pigments affect the color of reflected light
Explain how linearly polarized light is formed and detected

41. Key Ideas: Characteristics of Light
Light is electromagnetic radiation consisting of oscillating electric and magnetic fields with different wavelengths
Relationship between the frequency, wavelength, and speed of Em radiation is given by the equation c = fλ
Brightness of light is inversely proportional to the square of the distance from the light source

42. Key Ideas: Flat Mirrors
Light obeys the law of reflection, which states that the incident and reflected angles of light are equal, measured wrt normal to the reflecting surface
Flat mirrors form virtual images that are the same distance from the mirror’s surface as the object

43. Key Ideas: Curved mirrors
The mirror equation relates object distance, image distance, and focal length of a spherical mirror
The magnification equation relates image height or distance to object height or distance, respectively

44. 13.4 Color and Polarization
White light is a mixture of various colors of light
Colors of light correspond to different wavelengths of light
Dispersion of Light:
white light is separated into its various colors

45. Dispersion of light

46. Absorption of Light
Various things can happen to light when it encounters a medium
It can be
Reflected
Absorbed
Refracted
Transmitted

47. Colors of Objects Color of objects depend upon
What wavelengths of line shine upon the object
Which are absorbed
Which are reflected

48. What if a green plant was illuminated with red light?

49. Color
White light is composed of equal amounts of the primary colors, blue, green, and red
Blue, green, and red are additive primary colors because they produce white light when added together
Complementary colors (cyan, magenta, yellow) are formed by combination of two primary colors
These are known as subtractive colors because they produce black when added together

50. Primary (additive) and Complementary (subtractive) colors

51. Polarization of Light
As electromagnetic waves, light consists of oscillating electrical and magnetic fields at right angles to one another

52. Unpolarized Light
Although all the light waves have this perpendicular relationship
Different waves have different orientations

53. Polarized Light
It is possible to filter light so as to eliminate unwanted oscillations
This permits the passage of waves oscillating in only one direction
This is linear polarized light

54. Key Ideas: Color and polarization
Light of different colors can be produced by adding light consisting of the primary additive colors (red, green, and blue)
Pigments can be produced by combining subtractive colors (magenta, yellow, and cyan)
Light can be linearly polarized by transmission, reflection, or scattering