Download The Properties of Light and Color – What we see

The Properties of Light and Color
What we see and how we see it!
After reading this chapter summary of the properties of light and color, we
hope that you will understand the following objectives:
1. Why light is important in our world.
2. Describe the difference between luminous and non-luminous objects.
3. Represent light as a ray diagram.
4. Explain how we see light.
5. Define and classify objects as transparent, translucent, and opaque.
6. How a light source affects the type of shadow created.
7. Define and explain umbra and penumbra.
8. Predict how a pinhole will work.
9. Identify the primary colors of light and pigment.
10. Explain how primary colors combine to form all colors.
11. White light is all colors combined and black is the absence of light.
12. Explain how we see colored materials.
13. Use the Electromagnetic Spectrum to identify the most and least energetic
waves.
The following experiments should be conducted in order to reinforce your
understanding of light and color:
1. The Laser Lab:
Experimenting with lasers in several situations help you to understand the
properties of light and how light behaves. Comparing light bulbs in flashlights to
laser pointers and how they differ in different situations. You learn how to draw
ray diagrams for light, and learn that light is only visible when it reflects off
another object. By drawing these ray diagrams you learn how light spreads out in
all directions and that light travels in a straight line. One experiment with laser
pointers is spraying water into the air, and shining the laser into the mist. You’re
able to see bits and pieces of the red beam because it’s reflecting off of the
water in the air. This teaches you that light is not visible without material to
reflect off of. The one major safety precaution that we focused on in this lab was
safety with lasers, and ensuring that we wouldn’t shine a potentially blinding laser
into somebody’s eye, the rule being to never shine a laser in the direction of an
individual.
2. Pure water vs. Cloudy water
This experiment explores the idea of light going through interference. By
exploring how light acts when it interacts with pure water vs. cloudy water, we are
able to understand how light behaves in these situations. When interacting with
pure water, light passes through with extremely limited alterations, while when
interacting with cloudy water, some of the light beams reflect off the dust and
cloudiness from within the water, with less light passing through to the other side.
This experiment’s main safety precaution is that the students must be careful and
not drop the light (whether it is a flashlight or a bulb) in the water, with the
danger of electrocution occurring.
3. Light and Slits
In this experiment, students learn more properties of light, and how
shadows behave. Using slits, we can see how light can be filtered by slits, and how
slits can restrict the amount of light to pass onto a surface. While a point light
source would normally send light rays in all directions, creating a large spot of light
on a surface, the slit allows only a small fraction of the light from the point source
to hit the surface, creating a small dot of light. Slits also impact the amount of
light that went through from an extended source. You learn that slits invert the
shape of the filament from an extended light source.
4. A Light on the Wall
When you experiment with light on walls, you learn how light spreads out in
all directions. When you use a point source, it’s not just a point of light that shines
off the wall; it’s an expanded illuminated circle. Also, in the circle the center of
the circle is the brightest part and as you move away from the center the wall
becomes less and less bright.
5. Color filters
When experimenting with color filters, we learned about properties of light
and color, such as the primary colors of light and primary colors of pigment. We
experimented with the three different colored light bulbs (red, blue, and green)
and held up corresponding colors to see what we would view through them. We
discovered many different properties and how light acts with filters, and we
learned how different colors act in different situations. Some safety precautions
consisted of making sure you don’t drop a light bulb and not looking directly into
the light.
--------------------------------------------------------------------------------------------Every-day experiences that one can observe properties of light from are:
1. Green color reflected from grass and leaves into our eyes.
2. Light rays from the sun illuminating the Earth.
3. Lengths of shadows, and different shades of shadows.
4. Prisms and how they split up light to form rainbows.
5. Lamps illuminating an entire room.
6. Clouds blocking sunlight from passing onto parts of the earth.
LIGHT – GETTING UP CLOSE AND PERSONAL
One of the most important skills necessary in order to become proficient in
understanding light is being able to draw ray diagrams, and model how light travels
to understand how we see colors.
Ray diagrams can be used to show various aspects of light. One of the most
important is how they depict how we see light. We can use ray diagrams to show
how light rays go in a straight light from a light source to our eye, allowing us to
see the object. With these ray diagrams, we can model how light travels, whether
it is reflecting off a surface into our eye, or coming straight from a luminous
object, ray diagrams show us how we see light by showing how light moves. We use
ray diagrams to show the motion of light because when drawing ray diagrams, you
always draw rays in a straight direction with an arrowhead at the end, explaining
that the light is going on continuously. By using ray diagrams we can also show how
we see various colors, by drawing a ray and showing how it splits into different
colors (from white light) into different colors after interacting with an object with
colors of pigment. Rays can also be used with prisms, to show how light splits up
into many different colors due to many different frequencies.
Ray diagrams are drawn by starting from a point, whether it’s on a point
source or an extended light source, and drawing rays extending in all directions
from the light source, since light travels in all directions. Always ensure that your
rays are straight and they always have arrowheads on the end of them, as well as
making sure that they are extending in all directions.
Pinholes are extremely important objects that can be used to further
understand light. Pinholes allow only a certain amount of light to travel through it
and reflect off of the wall behind it. A pinhole doesn’t allow a lot of light through
it, but, rather just a small amount. When shining a light source onto a pinhole, the
light reflected off will be an expanded version of the light source, but inverted.
For example, if you shine a light bulb with an “L” shaped filament, the shape of
light reflecting off of the wall behind the screen after it filters the light will be
the shape of an “L” but rotated 180 degrees.
There are two different kinds of light sources, point sources and extended
sources. When using a point source, all light comes from a single point, rather than
when using an extended source which exerts light from extended points on the
extended source. Shadows created from a point source have just one shade of
shadow with the shadow being of complete darkness, while extended light sources
cause shadows to form with umbrae and penumbrae.
Umbrae and penumbrae are formed when an extended light source shines on
an object while there is another object in between the two. The umbra is the area
of complete darkness, or the absence of light, where absolutely no rays from the
light source are able to reach. The penumbra is formed by the areas of shadow,
but not complete darkness or complete exposure to light. Penumbrae are formed
when only part of the light source is capable of reaching the area. Whenever the
entire light source is unable to shine, but at least a small trace of light is capable
of reflecting off, the area is called a penumbra. Also, obviously, wherever the
entire light source is able to shine on, with no interference, the area is a region
with no shadows.
Objects on the world can be categorized in many different ways. Different
categories consist of luminous, non-luminous, transparent, translucent, opaque,
specular, and diffuse. Luminous objects omit light while non-luminous objects don’t,
and just reflect light. An example of a luminous object is molten rock, or simply a
light bulb, while an example of a non-luminous object is a desk, or a plate, which
doesn’t generate its own light, but reflects light, no matter how shiny it may seem.
Transparent objects allow all rays of light to pass through it, all direct and indirect
rays. Translucent objects only allow some light rays to pass through it, allowing
viewers to see the general shape of the object, while opaque objects allow
absolutely zero light rays through it. Examples of transparent, translucent, and
opaque objects are a window, wax paper, and a rock, respectively. Finally, specular
objects are mirror-like objects that are mainly flat and allow light rays to reflect
smoothly off it, creating a clear image, while diffuse objects are microscopically
rough, and reflect light rays in all directions.
The primary colors of light are red, green, and blue, while the primary colors
of pigment are magenta, yellow, and cyan. The secondary colors of light and
pigment are the same as the primary colors of the opposite, so the secondary
colors of light are the primary colors of pigment, and vice-versa. The primary
colors can be used to create all different shades of color, depending on the variety
of intensities and concentrations of color. More red and less blue or more green
and less red can allow light to create all the different colors of the spectrum. We
are able to see colored objects when white light shines on them because the object
absorbs certain colors while the other colors are reflected off of it. For example,
a cyan book would absorb the red light and reflect the blue and green light,
allowing the viewer to see cyan. Color filters play an important role in what colors
we see. A filter of any color allows only rays of light of the same colors through it,
and doesn’t allow any other colors through. If you were to hold up a red filter, all
white objects would seem red, since the filter would absorb the green and blue
light, while all red objects would stay red, and all other colored objects would seem
black, since the red filter would absorb the green and blue light, while only red
light would be allowed to pass, however there would be no red light so the object
would seem black due to the absence of light.
The electromagnetic spectrum is a tool that scientists use to compare
different colors of light, using their frequencies to set them apart. You can tell
how the spectrum is set up simply by using a prism and shining white light through
it, and seeing how the colors appear when they refract and go through the prism.
Red is the fastest, or most active, out of the colors in the spectrum, so it is bent
the most, while violet is the slowest, or least active, of the colors in the spectrum,
so it bends the least.
To interpret ray diagrams there are a few key things you must take into
consideration. First you must look to see that light is traveling in all directions.
Second you must see if the light rays are traveling in a straight direction. And
third you must determine where light is reflected, and where light doesn’t reach.
By determining these factors, you can understand what we see in the world and
how we see it.
When faced with problems that have to do with ray diagrams, first think the
problem through. After coming up with a simple plan of how to go about the
problem-solving, construct a ray diagram of what you think is happening in the
system. Use rays and pictures to determine the answer to what the question is
asking you, because all that you could ever be asked can be determined by drawing
a ray diagram. Remember, a ray diagram is a scientist’s best friend, because even
though human error exists, ray diagrams are too simple and direct to mess up!
Referring to the beginning objectives of this chapter, we shall review what we have
learned after going over several different aspects and properties of light. We’ve
learned:
1. Why light is important in our world.
Light is important in our world today because without it, we wouldn’t be able
to see anything or even exist on earth.
2. Describe the difference between luminous and non-luminous objects.
As previously mentioned, luminous objects omit light while non-luminous
objects do not.
3. Represent light as a ray diagram.
We’ve constantly reviewed how to represent light as a ray diagram, the
following questions will also help you to understand and view how ray
diagrams work.
4. Explain how we see light.
We’ve explained how light reflects off objects and into our eyes allowing
humans to see.
5. Define and classify objects as transparent, translucent, and opaque.
We’ve defined transparent objects to allow all light rays through,
translucent objects to allow some light rays through, and opaque objects to
allow no light rays through.
6. How a light source affects the type of shadow created.
We’ve learned that a point source creates one shade of shadow, with
complete absence of light or complete absence of shadow, while extended
light sources create umbrae and penumbrae.
7. Define and explain umbra and penumbra.
We’ve defined an umbra as an area of complete absence of light and a
penumbra as an area of some light and some shadow.
8. Predict how a pinhole will work.
We’ve understood how pinholes flip the light shining through it to rotate it
180 degrees, so either the dot from a point source or the filament shape
from an extended source will be rotated and shown on the wall behind the
pinhole.
9. Identify the primary colors of light and pigment.
We’ve identified the primary colors of light as red, blue, and green, while
primary colors of pigment are magenta, cyan, and yellow.
10. Explain how primary colors combine to form all colors.
We’ve understood how the primary colors of light are the primary colors of
pigment combined in certain combinations, and vice-versa, while different
concentrations of specific colors influence the colors created.
11. White light is all colors combined and black is the absence of light.
We’ve explained how white light is the combination of all colors and how it
can be split up into several different primary colors of light while we see
black when no light is reflecting off an object or all the light is absorbed.
12. Explain how we see colored materials.
We’ve understood that we see colored materials when certain objects
absorb certain colors and reflect others, which dictate which colors we see
after the light rays reflect off the material.
13. Use the Electromagnetic Spectrum to identify the most and least energetic
waves.
We’ve identified the rainbow as an easy way to remember the
Electromagnetic Spectrum as well as prisms and we’ve identified that red is
the most energetic and violet is the least energetic.
This concludes the written proportion of the review of the properties of light and
color. The upcoming review section will help refresh your mind allow you to interact
with these topics yourself. Questions will all be provided followed by all the
answers.
1.
Draw a ray diagram from the point source onto wall.
2.
Draw a ray diagram from the extended source onto the wall. Label the shadows
3.
Draw a ray diagram from the extended source onto the wall. Label the shadows
4.
What happens as the light travels from the point source through the pinhole?
5.
Is this an accurate illustration? What is happening to the shape of the filament?
6.
What color is the blue ball through the red filter?
7.
What color is the yellow ball through the green filter?
8.
What color is the blue ball through the blue filter?
9.
Explain why there are the different areas of shadow.
10.
What is being illustrated? Why is this event occurring?
11.
What would you consider the sun due to this ray diagram?
12.
Which bulbs can each person see?
13.
14.
Why shouldn’t you do so?
15.
16.
ANSWERS!!!
1.
2.
Top to bottom: penumbra, umbra, and penumbra
3.
Top to bottom: penumbra, umbra, and penumbra
4.
The light expands to form a larger box compared to the size of the pinhole.
5.
The illustration is correct; the shape of the filament is rotated 180 degrees
6.
The ball is black because no light is able to travel through the filter
7.
The ball is black because no light is able to travel through the filter
8.
The ball is blue because the blue light is able to pass through the filter
9.
There are different areas of shadow because the light source is an extended
source so some areas receive all light; others only receive some light, while others
receive no light.
10.
The Electromagnetic Spectrum is being illustrated and this is occurring because
different colors of light have different frequencies, so white light splits up when
it refracts through a prism.
11.
Even though the sun seems like a point to us on Earth, it’s still an extended light
source.
12.
Jason can see A and C, Joy can see A, B, and D, Bob can see A and C, and Xavier
can see A and C.
13.
The moon is not a luminous object. It may seem like one at night, but it’s only
reflecting the sun’s light.
14.
You could see a dot from the laser all around the walls, or you could step into the
laser beam. You wouldn’t do this because you could severely damage your eyes.
15.
Persons 2, 4, and 5 would be able to see it.
16.
No matter what, whenever you’re in a pitch-black room, you will never see anything