Electromagnetic
Waves
Electromagnetic
Waves
Waves consisting of
oscillating electric and
magnetic fields that move
at the speed of light
through space.
Electromagnetic Spectrum
Corresponding wavelength and frequency
Light
Light is the range of frequencies of the
electromagnetic spectra that stimulate the
retina of the human eye.
Wavelengths of Light Range from:
400 nm to 700 nm
.0000004 m to .0000007 m
Speed of Light
The story starts with:
Galileo Galilei
(1564 – 1642)
First to
hypothesize
that light
has a finite
speed
The story takes off with:
Ole Roemer
(1644 – 1710)
Determined the relative speed of
light by viewing the orbital period
of Io, a moon of Jupiter.
The period varied by 14 seconds,
depending on the Earths
approach.
Jupiter
Earth
Orbit
From this he calculated
it took 22 minutes for
light to travel across the
orbit of the Earth.
Today’s accepted value is
about 16 minutes
Jump to the twentieth century:
Albert Michelson
(1852 – 1931)
In 1926 Michelson was working
at the Mount Wilson
Observatory in Pasadena
California, when he calculated
the time light required to make
a round trip between two
California Mountains 35 Km
Determined the speed of light apart.
to be:
2.997996(0.00004) x10
8m
First American
to receive the
Nobel Prize
s
Sources of Light
Luminous Bodies –
Objects that emit light
waves. i.e. - Sun
Luminous Flux - P – Rate at
which light is emitted from a
source in all directions. Units
Lumen = lm
Candela – cd – Candle Power
– Measure of luminous
intensity
Illuminated Bodies –
Objects that reflect
light waves. i.e. - Moon
Illuminance – E – Measure of
the illumination of a surface.
Units Lux = lx Lumens per
square meter
Sources of Light
The Luminous Intensity of a point source is the
Luminous Flux that falls on one square meter of a
sphere one meter in radius.
Thus Luminous Intensity is
Luminous Flux divided by 4
P
measured in cd
I
4
Illuminance varies directly
with the flux of the light
source and inversely with the
2
square of the distance from
the source.

P
I
E
 2
4d
d
Transparent
Light waves are
transmitted through the
material
Translucent
Material that transmits
light but distorts the
path
Opaque
Material that does not
transmit light
Refraction of Light
Refraction – The change in direction or bending of light waves at the
boundary between two media.
Snell’s Law – A ray of light bends in such a way that
the ratio of the sine of the angle of incidence to the sine
of the angle of refraction is a constant.
For a light ray passing from a
vacuum into a given medium.
n1 sin  1  n2 sin  2
sin  i
n
sin  r
This constant n is the index of
refraction
For two media other than a vacuum
Refraction of Light
Indices of Refraction
Medium
n
Vacuum
1.00
Air
1.0003
Water
1.33
Ethanol
1.36
Lucite Plastic
1.49
Crown Glass
1.52
Quartz
1.54
Flint Glass
1.61
Diamond
2.42
Color is perceived because of a physiological
response to excitation by light of the cone
receptors in the retina of the human eye. The
cones are sensitive to light with wavelength of
400 nm to 700 nm. Different wavelengths of light
are perceived by the brain as different colors.
Primary Light Colors
RED
GREEN
BLUE
Secondary Light Colors
MAGENTA
CYAN
YELLOW
Additive Method of Color
Production
When light beams of the primary colors (red, blue and
green) are projected onto a white screen,, mixtures of
them produce other colors. Varying the intensities of the
beams allows different colors to be produced.
Red + Green = Yellow
Green + Blue = Cyan
Blue + Red = Magenta
Red + Green + Blue = White
Complementary Colors = Two colors that , when added produce
white light
Yellow + Blue = White
Magenta + Green = White
Cyan + Red = White
Pigments are colored material that absorb certain colors and transmit
or reflect others
Example – A tomato absorbs blue
and green light and reflects red
light, so it appears red. If only
blue light was projected on the
tomato it would appear black
A pigment that absorbs only one color from white
Note that the primary pigment
light is called a Primary
Pigment
colors are
the secondary light colors
and the secondary pigment colors
are the primary light colors.
Primary Pigments = Yellow, Cyan and
Magenta
A Pigment that absorbs two primary colors and
reflect one is a Secondary Pigment
Secondary Pigments = Red, Blue and
Green
Polarization
Orientation of the transverse oscillations of
light waves
Partially Polarized –
Some preferential
orientation
Plane or Linearly Polarized –
Orientation in only one plane