Download Wave - Particle Duality of Light some experiments indicate that light

LIGHT
Wave - Particle Duality of Light
some experiments indicate that light behaves like a wave
and others indicate that it behaves like a stream of
particles. No one has actually seen light waves - it is just
a model to explain the behavior of light.
Light is a source of energy. A source of light must produce or
transform energy.
Light is the range of frequencies of electromagnetic waves
that stimulates the retina of the eye.
Light is transmitted in straight lines.
Light from a source, such as the sun or a bare light bulb,
generally spreads out in all directions, in straight lines.
Light given off by a bulb can be concentrated into a beam
by a flashlight or spotlight.
Speed of light = 2.997996 x 10 8 m/s
Transparent object - where most of the light passes through;
objects can be seen clearly through transparent objects.
Ex. Clear glass and plastic.
Translucent object - the light is scattered; you cannot see
things clearly.
Ex. Frosted glass.
Opaque objects - you cannot see through opaque objects; the
light is absorbed or reflected by these materials.
Ex. Wood, brick, soil.
COLOR
One of the mot beautiful phenomena in nature is a rainbow.
Artificial rainbows can be produced by prisms.
In 1666, Newton did his first scientific experiments on the
colors produced when a narrow beam of sunlight passed
through a prism.
Newton called the ordered arrangement of colors from
violet to red a SPECTRUM.
Newton thought there was unevenness in the glass might be
producing the spectrum. To test this assumption, he allowed
the spectrum from one prism to fall on a second, reversed
prism. If the spectrum were caused by irregularities in the
glass, the second prism should increase the spread in colors.
Instead, a spot of white light was formed.
White light is composed of colors.
Colors of the spectrum are associated with specific light
wavelengths.
The color of the light is related to the wavelength or
frequency of the light (that to which our eyes are sensitive).
Wavelengths of light waves have a range of about 400 nm to
750 nm.
R
O Y
G
B
V
7x10-7
4x10-7 m
Why do we see colors?
•
many materials contain chemical substances called dyes
or pigments that absorb only certain wavelengths of light
and reflect others.
•
dye: molecule that absorbs certain wavelengths of light
and transmit or reflect others.
•
pigment: colored material that absorbs certain colors and
transmits or reflects others.
Primary Colors
White light can be formed from colored light in a number of
ways.
•
if correct intensities of red, blue, and green light
are projected on a white screen, the screen will
appear white. Thus R + B + G form white light.
•
when R, G, B light form white light, this is the
additive color process.
•
for this reason, R, B, G are primary colors of light.
•
the primary colors can be mixed in pairs to form
three other colors:
R+G
yellow
B+G
cyan (aqua)
R+B
magenta (purple)
These colors are called secondary light colors.
•
Black is the absence of reflected light.
•
Yellow is the absence of blue or opposite blue.
Therefore, yellow and blue will produce white light.
•
Cyan is opposite red and magenta is opposite green.
•
Any two colors that combine to produce white light are
complementary colors.
•
the subtractive color process: if you take yellow
away from white light, you get blue. Yellow,
magenta, and cyan are the subtractive primaries or
primary pigments.
•
red, blue, and green are secondary pigments.
Secondary pigments absorb two primary colors and
reflect one. Red absorbs green and blue and
reflects red.
Polarization
Light is a transverse wave that has two components. They are
perpendicular ( ⊥ ) to each other.
Polaroid material contains long molecules that allow
electromagnetic waves of one direction to pass while
absorbing the waves vibrating in the other direction.
Some material (polarizers) only allow one component to pass
while blocking the other. Therefore, the amount and intensity
is reduced.
ie. polarized sun glasses