LIGHT
A FORM OF
ELECTROMAGNETIC
RADIATION THAT STIMULATES
THE EYE
I. Electromagnetic Radiation
A. Light is a wave and therefore
has all the properties of waves.
B. Light waves have wavelengths
that range from 380nm to 760 nm
C. Studying light allows us to study
all electromagnetic radiation
D. White light is all colors mixed
together
E. Monochromatic light is light of
one color, a single wavelength or
frequency
The numbers listed
here are frequencies
not wavelengths to find
the wavelengths
Remember v=fλ
II.
Movement of light
A. Light travels in a straight line
B. The speed of light is constant in
a given medium (like the speed of
all waves within a medium)
C. Light travels fastest in a vacuum
(space)
D. Denoted by the symbol c, found on
the table of constants on reference
tables c= 3 X 108 m/s
This refers to all forms of electromagnetic
radiation not just visible light.
E. Electromagnetic Radiation is produced by
the movement of charged particles
F. In a material medium the speed of
light is always less than in a
vacuum.
1. it varies with
a. Optical density of the
medium
b. Frequency
G. The speed of light in air is very
close to the speed of light in a
vacuum, The same value is
generally used for both
III.
REFLECTION
A. Law of Reflection
1. Statement: When a light
ray is incident upon a
reflecting surface the angle of
incidence is equal to the angle
of reflection.
θi = angle of incidence θr angle of reflection
Normal is a line perpendicular to the reflecting surface
B.
Regular Reflection
1. Occurs when light hits a
polished surface (flat). This is
when the law of reflection applies
2. The reflected rays are all
parallel because normals are
parallel
C.
Diffuse reflection
1. occurs when light hits an
irregular surface.
2. The reflected rays are
scattered. Not parallel because
the normals are not parallel
IV.
REFRACTION
A. The bending (change in
direction) of light as it moves
from one medium to another.
B. The incident ray strikes the
boundary between two media. It
will change direction and
speed as it enters the new
medium.
C. When the angle of incidence is
zero, along the normal, the ray
passes straight through into the
θ1 is the angle the incident ray makes with the normal
(line perpendicular to surface)
θ2 is the angle the refracted ray makes with the normal
F.
D. Optical Density- property of a
medium that determines the speed
of light
1. the more dense the slower
the light will travel and vice versa
E. The refracted ray will bend
toward the normal when it enters
a more optically dense medium.
The refracted ray will bend away
from the normal when it enters a
medium that is less optically
dense.
Example of light entering a more dense medium.
The ray bend toward the normal and slows down
Example of a light ray entering a less dense medium and
bends away from the normal and speeds up
G.
Absolute Index of Refraction
1. More optically dense media
have a higher index of refraction.
2. Values are 1.00 or greater
3. represented by n
4. n=c/v
n = absolute index of refraction
c= speed of light in a vacuum,
3.0X108m/s
v= speed of light in a given
medium, m/s
5. Values on Reference Tables
H.
Snell’s Law
1. Gives the relationship between
angle of incidence and angles of
refraction to the index of refraction
2. n1sinθ1 = n2sinθ2
n1= index of refraction of incident
medium
n2 = index of refraction of refracted
medium
θ1= the angle of incidence
θ2 = the angle of refraction
I.
The relationship between index of
refraction, velocity and wavelength
is given by:
n2 = v1 = λ1
n1
v2
λ2
Where 1 represent medium 1 and 2
represents medium 2
Units v= velocity m/s λ = wavelength,m
n2/n1 is called the relative index of refraction.
J.
Critical angle
1. Definition- the measure of
the incident angle that causes
the refracted ray to lie right
along the boundary between
the two mediums.
2. unique to a substance.
3. To calculate, use Snell’s law and
substitute in 90 for the refracted
ray. n1sin θ1 = n2sin 90
AS θ1 INCREASES SO DOES θ2, UNTIL IT IS EQUAL TO 90. THEN THE
REFRACTED RAY MOVES ALONG THE BOUNDARY OF THE 2 MEDIUMS
K.
Total internal reflection
1. occurs when the critical angle is
exceeded, light can no longer
escape and is reflected back into
the medium.
2. Law of reflection applies here
V.
Dispersion
A. As light enters a medium each
wave of different frequency (color)
travels at different speeds.
B. When white light falls on a
prism, the waves of each
frequency refract by different
amounts, separating the colors.
C. Red light refracts the least
because red light has the highest
velocity in glass. Violet the most.
VI.
Polarziation of Light
A. Def: Separation of a beam of
light so that the vibrations are in
one plane.
B. Property of transverse waves.
C. Light can be polarized so it
must be a transverse wave.
Doppler and light
When an object emitting light (like a
star) is moving away from another
object (like the earth) the
wavelength of light appears to be
getting longer which means that the
color of the light is shifted toward the
red end of the spectrum. This is
what is meant by red shift.
Conversely if an object is moving
toward another then the shift is
toward the blue end of the spectrum.
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