Transcript Optics

Light and Optics
Chapter 22, 23
Light as an Electromagnetic wave
 Light
exhibits behaviors which are
characteristic of both waves and particles

Interference, Doppler effect
 Electromagnetic
waves are waves of
changing electrical and magnetic fields.



A changing electrical field will produce a
magnetic field.
They travel at 3.00*108 m/s
First detected by creating a rapidly moving
electrical charge and detecting the magnetic
field a distance away by using a loop of wire.
Electromagnetic spectrum
 Electromagnetic
waves can be produced
over a wide range of frequencies
 Other EM waves:

Radio, microwaves, infrared, ultraviolet,
x-rays
Practice
 Calculate
the wavelength of a 60Hz EM
wave, a 93.3 MHz FM radio wave, and a
visible red laser of 4.74*1014 HZ
 5.0*106m,
3.22m, 6.33*10-7m
Speed of light
 First
attempted by Galileo using mirrors
 Ole Roemer used the period of a moon in
Jupiter's Orbit to prove the speed of light
was finite.
 Albert Michelson Used a rotating mirror
and light source to finally prove light
moves at a speed of 2.9979*108m/s or
3.00*108 m/s.
The ray Model of light
 Light

travels in …
Straight lines
 The
straight line paths that light travel in
are called Rays
 Light travels in every direction from the
source.
 Geometric optics-describing aspects of
light by using the ray model
 See smartbook nots
Refraction
 Index





of Refraction
Light travels at c = 3.00 *10 8 m/s in a vacuum
The speed decreases as it passes through
other substances.
The ratio between the speed of light in a
vacuum and the speed of light in another
substance is called the index of refraction
n=c/v
The higher the index, the slower light is
traveling
Refraction


Refraction is the bending of light
Light bends toward the normal when passing
into a more dense medium (higher n value)
 Light bends away the normal when passing into
a less dense medium (lower n value)
Angle of incidence is often
written as Θ1
Angle of refraction is often
written as Θ2

Light bends more as the angle of incidence
increases.
Snell’s Law
 The
angle of refraction depends on the
speed of light in the two media and the
angle of incidence
 n1 (sin Θ1) = n2 (sin Θ2) (Snell’s Law)

Known as the law of refraction
Example

Light strikes a flat piece of glass at an incident angle of
60.0 o . In the index of refraction of the glass is 1.50
What is the angle of refraction in the glass, and at what
angle does the ray emerge from the glass?
Total internal Reflection
 When
light passes from a more dense
material to less dense material, at a
particular incident angle the light will skim
across the surface.


This angle is the critical angle
Sin Θc = n2 / n1
 For
any incident angle greater than this,
no light is refracted and there is total
internal reflection.
Total internal Reflection
 Many
optical instruments such as
binoculars use total internal reflection.


Prisms are used to reflect light
Better than using mirrors because less light is
lost.
 Fiber
optics- glass or plastic fibers that
internally reflect light to transmit it from
one place to another.


Telecomunications
Medical
• Bronchoscope
Physics of Diamonds

Diamonds achieve their brilliance partially from total
internal reflection. Because diamonds have a high index
of refraction (about 2.3), the critical angle for the total
internal reflection is only about 25 degrees. Incident light
therefore strikes many of the internal surfaces before it
strikes one less than 25 degrees and emerges. After
many such reflections, the colors in the light are
separated, and seen individually.