Electromagnetic waves consist of oscillating electric and magnetic fields perpendicular to each other that propagate through space carrying electromagnetic radiant energy. The electromagnetic spectrum ranges from gamma rays to radio waves and includes visible light, which is a small portion of the full spectrum. Electromagnetic waves travel at the speed of light and their wavelength and frequency are related by the equation that defines the speed of light. Reflection and refraction of light can be described using laws of optics and ray diagrams. Reflection occurs when light changes direction upon contact with a new medium, and refraction is the bending of light that occurs when passing from one medium to another due to the speed of light changing.

3. Electromagnetic Waves
 Magnetic field wave perpendicular to an electric field wave
 All objects emit EMWs.
  Temp EMW
 Electromagnetic spectrum
 Range of all frequencies of light
 Visible light is a very small portion of that entire spectrum.

5. c
 Speed of Light - 3.00 x 108m/s.
 = (wavelength) x (frequency)
 c = ƒ

6. Example
AM Radio waves
5.4 x 105 Hz
1.7 x 106 Hz
 = ?

7. Visible Light
Part of the EMS humans can see
Red - 750nm (x10-9m)
Purple - 380nm
Bees, Birds – UV
Snakes – IR

8. Reflection
Light waves usually travel in straight paths
Change in substance changes direction
Opaque - does not permit light
some light reflected
some light absorbed as heat

9. Reflection
Texture affects reflection
Diffuse reflection (rough)
 reflects light in many different directions,
Specular reflection (smooth)
reflects light in only one direction
Smooth – variations in surface  

11. Mirrors
 Light striking a mirror reflects at the same angle that it struck
the mirror

12. Flat Mirrors
p = q
p- objects distance to the mirror
q - distance from the mirror to the image
Virtual image
Does not exist
Made by our eyes

14. Ray Diagrams
 Used to predict the location of the image of an object

15. Concave Spherical Mirrors
Reflective surface is on the interior of a curved surface
C – center of curvature
R – Radius (distance to C)
f – Focal Point (1/2 R)
Principal axis
any line that passes through C
usually oriented with an object

17. Mirror Equations
1/object distance + 1/image distance = 1/focal
length
1/p + 1/q = 1/f
Magnification (M) =
Image height/object height (h / h)
- (q / p)
• M = h / h = - (q / p)

18. Sign of Magnification
Sign of M
Orientation of
Image
Type of Image
+ Upright Virtual
– Inverted Real

19. Concave Spherical Mirror Rules
 A ray traveling through C will reflect back through C
 A ray traveling through (f) will reflect parallel to the PA
 A ray traveling to the intersection of the PA and the mirror will reflect at
the same angle below the PA.
 A ray traveling parallel to PA will reflect through the focal point

20. Ray Diagrams
Draw three rays
The image forms at the point of intersection
Example
f = 10.0cm
p = 30.0cm
h = 3.00cm

21. Convex Spherical Mirrors
Reflective surface is on the outside of the curve.
The points f and C are located behind the
mirror
negative

23. Rules
A ray parallel to the PA will reflect directly away from f.
A ray towards f will reflect parallel to the PA
A ray towards C will reflect directly away from C.
A ray to the intersection of PA and mirror will reflect at the same
angle below the OA.
Trace the 3 diverging lines back through the mirror to reveal the
location of the image which is always virtual

25. Example
f = -8.00cm
p= 10.0cm
h = 3cm

26. Parabolic Mirrors
Rays that hit spherical mirrors far away from the OA often
reflect though other points causing fuzzy images, spherical
aberration.
Telescopes use parabolic mirrors as they ALWAYS focus the
rays to a single point.

28. Refraction
Substances that are transparent or translucent allow light to
pass though them.
Changes direction of light
Due to the differences in speed of light

29. Analogy
 A good analogy for refracting light is a lawnmower
traveling from the sidewalk onto mud

30. Index of Refraction (n)
The ratio of the speed of light in a
vacuum to the speed of light in a
medium
 n -  c

33. Snell’s Law
ni(sini) = nr(sinr)
r = sin-1{(ni/ nr)(sini)}
Example
i = 30.0⁰
ni = 1.00
nr = 1.52

35. Total Internal Reflection
 If the angle of incidence of a ray is greater than a certain critical
angle the ray will reflect rather than reflect
 This principal is responsible for the properties of fiber optic
cables.
 Remember the lawn mower analogy…

37. Critical Angle
sin Θc = nr / ni
As long as nr < ni
What is the critical angle for light traveling from
Diamond to Air?

38. Thin Lenses
 Converging
 Diverging
 f- curve of lens & index of refraction

39. Converging Lens Diagram
1. Ray parallel to PA, refracts through far focal point
2. Ray through center of lens, continues straight line
3. Ray through near focal point, refracts through lens, continues
parallel to PA
 Treat lens as though it were a flat plane.

41. Diverging Lens Diagram
 Because the rays that enter a diverging lens do not intersect a virtual
image is formed by tracing back the refracted rays.
 Ray 1 - parallel to PA, refracts away from near f, trace back to near f.
 Ray 2 - ray toward far f, refracts parallel to PA, trace back parallel to PA
 Ray 3 - ray through center, continues straight, trace back toward object

43. Sign Conventions for Lens
Sign p q F
+ Near side
of lens
Far side of
lens
Convergin
Lens
– Far side of
lens
Near side
of lens
Diverging
Lens

44. Converging Lens Example
p = 30.0cm
f = 10.cm

45. Diverging Lens Example
p = 12.5cm
f = -10.0cm