Chapter 22 & 23: Light & Optics
Rules of the Light Ray Model:
A light ray is a line in the direction that light energy flows.
1. Light travels through a transparent medium in straight lines, called light rays at speed
___________, where n is the ____________________________ of the medium and c is the
_______________________ (3.0x108m/s).
Explain: Why does it take longer for light to travel through a medium then through a
vacuum?
2. Light rays do not interact with each other.
3. A light ray _________________ unless it has an interaction with matter that causes the
ray to change directions or to be absorbed.
4. Light has four different ways in which it can interact with matter.
Reflection
Refraction
Scattering
Absorption
Ray Diagrams:
 An object is a source of light rays. We make no distinction between self-luminous
objects and reflective objects.
 Rays originate from every point of the object, and each point sends rays out in all
directions.

A ray diagram that shows _______________________. A ray diagram does not imply that
these are the only rays.

Luminous objects give off an _____________________of light rays in all directions.

Our minds locate the object by sensing the point where the lines would diverge from.
Law of Reflection (equation & picture)
Reflections in a mirror: (ray diagram picture)
How big does a mirror have to be in order to see your entire length in it?
Why does light from the sun or moon appear as a column when reflected from a body of
water?
Refraction
Refraction –
Snell’s Law of Refraction:
Index of Refraction for common substances:
Air =
Glass =
Water =
Total Internal Reflection
 All the light will reflect from the surface.
 None of the light will refract (escape)
Critical Angle –
Example: Calculate the critical angle for ________ to air.
Example: Calculate the critical angle for air to _________.
Example: Calculate the critical angle from glass (n = 1.5) to _______.
Application of total internal reflection:
 Fiber Optics
Lenses
Ray Diagrams for Converging (convex) Lenses:
1. _________ incoming light is refracted through the ________________
2. Light coming in through the _________________ is refracted out _____________
3. Rays passing through the center are refracted out in the same direction.
4. An image is formed where the rays _____________.
Example: A parallel beam of light is sent through an aquarium. If a convex glass lens is held
in the water, it focuses the beam… (1) closer, (2) same, (3) farther … than before. Explain.
Example: Real Image -
Example: Virtual Image -
Lens Equations:
Distance Equation:
Sign Conventions:
Distances:
Symbol
Magnification Equation:
Magnification:
Front
Object
Location
Image
Location
Focal
Length
The light hits the front side
of a lens first.
Back
Symbol
Object Height
Upright
Image
n/a
Inverted
Image
n/a
Image Height
Magnification
If M < 1 then the image is SMALLER than the object
If M > 1 then the image is LARGER than the object
Optics and Your Eye
The only thing you can see is light.
 In order to see light, the light must _________________________.

If no light enters your eyes, you will see _________________________.

What can you see in a dark room? ________________

Why are shadows back?
__________________________________________________________________
The eye “sees” an object when bundles of diverging rays from each point on the object
enter the pupil and are focused to an image on the retina.

Farsighted
Sketch of farsighted eye:



 To correct:
Nearsighted
Sketch of nearsighted eye:



 To correct:
Example: A person who sees more clearly under water than in air without eyeglasses is…
Why?
Example: Are fish nearsighted or farsighted in air?