1. Geometric Optics
AP Physics
Chapter 23

2. Geometric Optics
23.1 The Ray Model of Light

3. represents a narrow beam of light
23.1 The Ray Model of Light
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
23.1

4. We see an object when rays of light come from the object to our eyes
23.1 The Ray Model of Light
We see an object when rays of light come from the object to our eyes
23.1

5. 23.2 Reflection: Image Formation by a Plane Mirror
Geometric Optics
23.2 Reflection: Image Formation by a Plane Mirror

6. When light strikes an object it is Reflected – bounces off
23.2 Reflection
When light strikes an object it is
Reflected – bounces off
Refracted – transmitted through
Absorbed – converted to a different form of
energy
Law of Reflection
23.2

7. Diffuse Reflection – on a rough surface Rays don’t form an pattern
We see color
Specular Reflection –
smooth surface
Patterns form images
23.2

8. How are images formed Your eye sees the intersection of rays
23.2 Reflection
How are images formed
Your eye sees the
intersection of rays
from an object
Applet
23.2

9. Object Distance – from mirror to the object
23.2 Reflection
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
23.2

10. 23.3 Formation of Images by Spherical Mirrors
Geometric Optics
23.3 Formation of Images by Spherical Mirrors

11. 23.3 Formation of Images by Spherical Mirrors
Spherical Mirrors – form a section of a sphere
Convex – reflection on outer
surface of sphere
Concave –
reflection on
inner surface
of sphere
23.3

12. 23.3 Formation of Images by Spherical Mirrors
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
23.3

13. 23.3 Formation of Images by Spherical Mirrors
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
23.3

14. 23.3 Formation of Images by Spherical Mirrors
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
23.3

15. 23.3 Formation of Images by Spherical Mirrors
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
23.3

16. 23.3 Formation of Images by Spherical Mirrors
Curved Mirror Equations
ho-object height
hi-image height
do-object distance
di-image distance
The Mirror Equation
Magnification
23.3

17. 23.3 Formation of Images by Spherical Mirrors
Sign Conventions
Image Height
+ upright (virtual)
- inverted (real)
Image and Object Distance
+ front of mirror
- behind mirror
Magnification
+ upright image
- inverted image
23.3

18. 23.3 Formation of Images by Spherical Mirrors
Sign Conventions
Focal Length
+ concave mirror
- convex mirror
23.3

19. Geometric Optics
23.4 Index of Refraction

20. 23.4 Index of Refraction
Index of Refraction – the ratio of the speed of light in a vacuum to the speed in a given material
Material
Index
Vacuum
NaCl
1.54
Air at STP
Polystyrene
1.57
Water
1.33
Flint Glass
1.65
Quartz
1.46
Sapphire
1.77
Crown Glass
1.53
Diamond
2.417
23.4

21. Value can never be less than 1
23.4 Index of Refraction
Value can never be less than 1
Material
Index
Vacuum
NaCl
1.54
Air at STP
Polystyrene
1.57
Water
1.33
Flint Glass
1.65
Quartz
1.46
Sapphire
1.77
Crown Glass
1.53
Diamond
2.417
23.4

22. 23.5 Refraction: Snell’s Law
Geometric Optics
23.5 Refraction: Snell’s Law

23. 23.5 Refraction: Snell’s Law
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)
23.5

24. 23.5 Refraction: Snell’s Law
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
23.5

25. 23.5 Refraction: Snell’s Law
Refraction occurs when one side of the wave slows down before the other
23.5

26. 23.6 Total Internal Reflection; Fiber Optics
Geometric Optics
23.6 Total Internal Reflection; Fiber Optics

27. 23.6 Total Internal Reflection; Fiber Optics
When light travels into a more 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
23.6

28. 23.6 Total Internal Reflection; Fiber Optics
Above the critical angle, light reflects following the law of reflection
Used in fiber optics
23.6

29. 23.7 Thin Lenses; Ray Tracing
Geometric Optics
23.7 Thin Lenses; Ray Tracing

30. 23.7 Thin Lenses; Ray Tracing
Thin lens – very thin compared to its diameter
Diagrams are similar to mirrors
Converging – rays converge
23.7

31. 23.7 Thin Lenses; Ray Tracing
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
Converging Lens
23.7

32. 23.7 Thin Lenses; Ray Tracing
Diverging Lens – spreads apart rays of light
Only produces virtual images
Rules
Parallel rays refract
away from F’
Rays headed toward
F refract parallel
Rays through O do not
refract
23.7

33. 23.8 The Thin Lens Equation; Magnification
Geometric Optics
23.8 The Thin Lens Equation; Magnification

34. 23.8 The Thin Lens Equation: Magnification
Equations are similar to Mirrors, conventions are different
The Thin Lens Equation is
To Calculate Magnification
23.8

35. 23.8 The Thin Lens Equation: Magnification
Conventions
Focal Length
+ converging lens
- diverging lens
Object Distance
+ same side as original light
- different side (only when more than 1 lens)
23.8

36. 23.8 The Thin Lens Equation: Magnification
Conventions
Image Distance
+ opposite side from light
- same side as light
Height
+ upright
- upside down
23.8

37. 23.9 Combinations of Lenses
Geometric Optics
23.9 Combinations of Lenses

38. 23.9 Combinations of Lenses
Many devices used combinations of lenses
Combination problems are treated as separate lenses
Calculate or draw the image from the first lens
Applet
23.9