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Transcript red - TeacherWeb

It’s a Rainbow
Kinda World!!
Prisms
• Prisms break white light into a rainbow by
refraction. Light goes in at an angle and
bends.
• Different frequencies (of which white light is
made) bend at different angles. So, the colors
of light fan out.
Prism and different wavelengths
(or frequencies):
Here are the average wavelengths of
the rainbow colors of light
Red
650 nm
Orange
590 nm
Yellow
570 nm
Green
510 nm
Blue
475 nm
Indigo
445 nm
Violet
400 nm
A nanometer = 1/billionth of a meter
• Different frequencies of light we can see, give
us the different colors of the visible light
spectrum. Together they make white light.
ROY G. BIV
Lasers…
are made of only one frequency of light in which all
the waves are “in step”.
White light, red laser, blue laser
When light meets a barrier
it can be….
• transmitted (go through)
• absorbed (stay in it)
• reflected (bounce off it)
Objects that…
• transmit most of the light are transparent
• scatter light as it passes through are
translucent
• reflect or absorb most of the light are opaque
When white light strikes an object
All the frequencies of light (ROY G BIV) are
absorbed, except for the one that bounces
back to your eye.
This red car appears red to you because the car
absorbs OY G BIV, and reflects the R back to
your eye.
• This black bowling ball absorbs all the colors
and none are reflected to your eye. Black is
the ABSENCE of light coming to the eye.
• The white bowling pins absorb none of the
light and all the colors are reflected back to
your eye. White is all the colors of light
combined.
Shining colored light: if red, the apple can reflect red,
with green or blue light, there is no red to reflect!
Your turn…
1. Figure out what happens when the primary
colors of light are mixed in different
combinations.
2. What happens when primary light is shined
on your rainbow?
Materials: flashlights, color paddles,
cellophane, rubber bands or anything else
you can think of.
In your composition book
• Design a lab to answer the previous questions.
Purpose
Prediction
Materials
Procedure
Observations (lends itself to a chart)
Conclusion
Mixing light
Primary
colors:
Blue
Green
Red
Secondary
colors:
Magenta
Yellow
Cyan
red
magenta
yellow
white
blue
green
cyan
How we see
Light enters through the
cornea and then the pupil,
with the iris controlling the
amount of light.
It goes through the lens,
inverting the image.
(Hopefully) it falls directly
on the retina.
The retina’s photoreceptor
cells are stimulated by the
frequencies of light.
Finding your blind spot
What creates it?
X
The “X” should be about 5 cm away. Cover your left eye and put
the card at arm’s length with the dot in front of your right eye.
Stare at the dot and bring the card toward you until the “X”
disappears.
Correcting
vision
problems
Peripheral Vision
P
O
E
X
How we see
Light enters through the
cornea and then the pupil,
with the iris controlling the
amount of light.
It goes through the lens,
inverting the image.
(Hopefully) it falls directly
on the retina.
The retina’s photoreceptor
cells are stimulated by the
different wavelengths of
light.
Seeing color and
light and dark
Cones respond to color:
Red cones
Blue cones
Green cones
Rods respond to:
Light and dark
Combinations of these receptors
help us to see all the different
colors.
Why do objects appear only in
gray tones in low light
situations?
The three kinds of cones respond
to these frequencies:
According to this graphic, why do we make
tennis balls chartreuse (yellow-green)?
Color blindness: How do
you suppose it happens?
The test to the left is
simple.
The individual with normal
color vision will see a 5
revealed in the dot
pattern.
An individual with
Red/Green (the most
common) color blindness
will see a 2 revealed in the
dots.
About 12-20% of white
males are colorblind.
How about some optical illusions,
just for fun?!
Stare at the dot up top for 30 seconds. Then look at
the lower dot. This is called an after image.
Stare at the center of the flag and for 1
minute and then look at a white sheet of
paper.
(physiological illusion: after image)
Count the black dots!
(a physiological illusion)
How many colors do you see?
There are only 3 colors: White, green, and pink.
There seem to be two different shades of pink,
but there is only one pink. (Cognitive illusion: color constancy)
Free powerpoint template:
www.brainybetty.com
31
Test what happens when you mix
pigments
• What colors do you seem to get mixing the
various primary colors of pigments?
• Why would this be different than mixing light?
Mixing pigments
green
cyan
yellow
red
black
magenta
blue
With filters: since the filters are transparent they only
transmit their own color. The red reflecting from the
apple cannot “get through” the green or blue filter.
Behaviors of Waves
•
•
•
•
•
Refraction
Reflection
Diffraction
Interference
Absorption
What can you tell me about these?
Refraction
Bending of light waves as it goes in at an angle
and changes speed going from one medium to
another.
Lenses are based on this.
2 Common Lenses
Convex lens
Reflection
Law of Reflection:
angle of incidence = angle of reflection
Regular reflection
Diffuse reflection
Kinds of Mirrors
• Plane mirrors
• Concave mirrors
• Convex mirrors
So, waves can be reflected,
transmitted (sometimes refracted),
and……
Absorption
Waves enter an
object, but do not
exit.
Energy of the
wave is transferred
to the particles in
the object and
transformed into
thermal energy.
Should have worn a
black sweater!
Diffraction
Here are some water waves passing…
through a slit
Image from upscale.utoronto.ca
around an object or end of a
barrier
Image from thestargarden.co.uk
Interference
Interference resulting from
diffraction
Image from astro-canada.ca
Constructive interference
Image from astro-canada.ca
The end