Transcript Geometric Optics

Physics Projects
1.
2.
3.
4.
5.
6.
Color wheel
Types of mirrors and uses
electromagnetic wave model
Reflection telescope model
Refraction telescope model
Build a 15, 10, and 5 seconds
pendulums
7. Research and explain rainbow
Due Sunday April 22nd.
CHAPTER 14
REFRACTION
Ms. Hanan
Chapter 14 Overview
14-1 Refraction
Investigate which direction light will bend when it enters another
medium and uses Snell’s law to solve problems.
14-2 Thin lenses
Solves problems involving image formation by converging and
diverging lenses using ray diagrams and the thin-lens equation,
explores eye disorders and eyeglasses, and examines the positioning
of lenses in microscopes and refracting telescopes.
14-3 Optical phenomena
Calculates critical angle; predicts when total internal reflection will
occur; explains atmospheric phenomena, including mirages and
rainbows; and briefly describes lens aberration.
14-1 Refraction
Objectives:
• Recognize situations in which refraction
will occur.
• Identify which direction light will bend when
it passes from one medium to another.
• Solve problems using Snell’s law.
Vocabulary
•
•
•
•
•
•
Refraction
Index of Refraction
Medium
Bending of a Wave Front
Angle of Incidence
Angle of Refraction.
Review
1.Wave speed equals
frequency times wavelength.
2.Reflection is the
turning back of an electromagnetic wave at a
surface of a substance.
3.The focal point is
the point at which a beam parallel to the principal
axes will converge after reflection from a concave mirror.
4.The focal length is
the distance from the focal point to the mirror.
5.Spherical aberration is an effect in which the
image produced by
a spherical mirror is blurred. It results from light rays converging
at different points when the mirror is not parabolic.
What is Refraction?
normal
air
θi
glass
block
θr
θi
θr
normal
air
The bending
of light as it
travels from
one medium
to another
Refraction
(bending light)
Light moves at different speeds
through different media. When it
travels from one medium into
another, the change in speed
causes the ray to bend.
normal
air
When light traveling through air
passes into the glass block it is
refracted towards the normal.
When light passes back out of the
glass into the air, it is refracted
away from the normal.
The wavelength of the light in the
glass is shorter than the
wavelength of the incoming light in
the air.
θi
glass
block
θr
θi
θr
normal
air
The Law of Refraction
The angle of refraction is related to the different speeds:
sin  i sin  r

c
v
The speed of light in a medium is given by the index of refraction of that
medium:
c
n
v
The Refraction of Light
Here are some typical indices of
refraction:
The Refraction of Light
We can now write the angle of refraction in terms of the index of refraction:
ni sin i  nr sin  r
The Refraction of Light
If light enters a medium of lower index of refraction, it will be bent away from
the normal. If the angle of incidence is large enough, the angle of refraction is
90°; at larger incident angles the light will be totally reflected.
The Refraction of Light
Basic properties of refraction:
http://phet.colorado.edu/en/simulation/bending-light
Sample Problem
A light ray of wavelength 589 nm (produced by a
sodium lamp) travelling through air strikes a
smooth, flat slab of crown glass at an angle of
30.0O to the normal. Find the angle of refraction θr.
Given:
 i  30 .0

ni  1.00
nr  1.52
Unknown:
r  ?
Solution
Use the equation for Snell’s law.
ni sin  i   nr sin  r 
 ni

1 1.00
 
 r  sin  sin  i   sin 
sin 30.0 
1.52

 nr


 r  19.2
1


Assignments
• Class-work:
Practice A, page 493, questions: 1, 2, and 3.
Refraction concept review worksheet.
• Homework:
Section review, page 493, questions: 1, 2, 3, and 4.
Refraction Problem A additional practice odd
questions.
Homework due next class