Transcript Summary Lecture 17 - Ohio State University

Summary Lecture 17
Wavefronts and
Snell’s Law of Refraction
Smaller velocity
Wavefronts closer together
Change in direction
Refraction
Normal
1
Medium 1 (n1)
2
Medium 2 (n2)
Caused by the difference in the speed
of light in medium 1 and 2
Index of Refraction n = c/v
(nair ~ 1, nWater = 1.33 …)
Snell’s Law of Refraction
n1 sin 1 = n2 sin 2
Example
A ray of light passes from air (n = 1.0)
into glass (n = 1.52) and then into Jell-O.
The incident ray makes a 58.0o angle
with the normal as it enters the glass and
a 36.4o angle with the normal in Jell-O.
What is the index of refraction in Jell-O?
Glass Jell-O
58.0o
36.4o
Total Internal Reflection
going from a medium with large n to
a medium with small n
“refracted” away from normal
1
2
c
n2
3
4
n1
Critical Angle: sin C = n2/n1
 > C
Total Internal Reflection
Lenses
Lenses refract light in such a way that
an image of the light source is formed.
Two prisms cause incoming parallel light rays
to change direction toward the principal axis
Think of a lens as a combination of many prisms
with “optimized” shape (spherical instead of flat)
With a convex lens parallel light converges to the
focal point.
Ray Tracing for Lenses
Converging Lenses (convex)
Diverging Lenses (concave)
Conventions
• Focal Length
• f is positive for converging lens
• f is negative for diverging lens
• Focal Length
• f is positive for converging lens
• f is negative for diverging lens
Conventions
• Focal Length
• f is positive for converging lens
• f is negative for diverging lens
• Object Distance
•do is positive if object is to the left of the lens
•do is negative if object is to the right of the lens
• Image Distance
•di is positive if object is to the right of the lens
•di is negative if object is to the left of the lens
• Object and Image Size
•ho, hi are positive if above the principal axis
Image Characterization
• Type: the image is real if di is positive
• Orientation: the image is upright if hi and ho
have the same sign
• Size:
the image is reduced if | hi | < | ho |
Thin Lens Equation
1
1 1


f do d i
Magnification Equation
hi
di
m

ho
do