Transcript Chapter 18: Ray Optics

Chapter 18: Ray Optics
Lisa Lerman
Becky Loock
Ray Model of Light

Light rays travel in straight lines
 Light rays cross but do not interact
 Light rays travel forever unless they interact with
matter
 Object is a source of light rays
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Point source– comes from one point (laser)
Extended source– collection of points (light bulb)
Light sees by focusing a group of rays

The eye inverts the object, but the brain flips it back
upright
The Pinhole Camera
A
light proof box has a single hole
 Film sensitive to light is placed at the back
 Each point on the object illuminates a
single point on the film
 The image is inverted
Types of Reflection
 Specular-
Reflection off of a smooth
surface (mirror)
 Diffuse-
Reflection off of a jagged surface
Reflection
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Angle of incidence = Angle of reflection
Angle of incidence- angle between the ray and the line
perpendicular to the surface (normal)
Angle of reflection- angle between the reflected ray and
the normal
Plane Mirrors
A
plane mirror is a flat mirror
 s’ = s
 The rays bouncing off the mirror enter our
eye, but we see if behind the mirror, at A’
Refraction

The bending of light
when it moves from
one medium to
another
 Snell’s Law- the angle
of refraction depends
on the refractive index
(n) of the medium

the angles used are
always from the
normal
Total Internal Reflection


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When all the light reflects back into the medium
Critical angle- the angle the light must refract at in order
to have total internal reflection
Critical angle when theta2 = 90 degrees
There is no TIR if n2 > n1
Dispersion

Dispersion- index of
refraction varies
slightly with color


This means it varies
slightly with
wavelength
N is larger when the
wavelength is shorter

Violet light refracts
more than red light
Thin Lenses

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Lens- transparent material that uses refraction of life at curved
surfaces to form an image
Ray tracing- the pictorial method to finding an image
Converging lens- Causes the ray to refract towards optical axis

Thicker in the middle
Focal point- Common point through which initially parallel rays pass
Focal length- distance from the lens to the focal point
Diverging lens- Causes rays to refract away from optical axis

Thinner in the middle
Virtual image- has the same orientation of the object
Real image- inverted from the image
RAY
TRACING!!!!
Converging Lens
Real Image
1
3
2
1. Parallel to optical axis and bends through far focal point
2. Through near focal point and bends parallel to optical axis
3. Through the center of the lens and does not bend
Converging Lens
Virtual Image
To draw the rays you follow the same rules as before. However, the rays
never meet, so you trace them backwards to find where they will intersect.
Diverging Lens
Virtual Image (ALWAYS!)
Follow the same rules and trace backwards to find where the rays meet
Concave Mirror
Real Image
1
3
2
1. Parallel to optical axis, reflects off and goes through focal point
2. Goes through focal point and reflects parallel to axis
3. Goes to center and reflects at the same angle
Concave Mirror
Virtual Image
Follow the same rules and extend backwards to see where rays meet
Convex Mirror
Virtual Image (ALWAYS!)
Follow the same rules and extend backwards to find where rays meet
Now try problem 15
on page 611, and 29
on page 612
Good Luck on the Final!
BYEEEE!