CHAPTER 4 Light

CHAPTER 4Light

Look carefully at the cups. What is the main difference among them?

Light and Color

• Transparent materials– Transmit most of the light that strikes it– See clearly through

• Translucent Materials– Scatters light as it passes through– Can see through it w/ fuzzy/blurred details

• Opaque Materials– Reflects or absorbs all of the light that strikes it– Light can’t pass through it

Transparent

Translucent

Opaque

If you know how light interacts with objects…

• You can explain why objects have different colors

The color of any object…

• Depends on the material of object and color of light striking it.

Rememeber: Wavelength:

Although light from the sun appears colorless or "white" it actually contains a range of colors

similar to a rainbow. You can see these colors using a prism to separate them out.

Color of opaque objects

• They are the color of the light they reflect.

A green object such as a leaf reflects only those wavelengths that create the visual effect of green. Other colors in the light are absorbed by the leaf.

White objects reflect most of the wavelengths of light that strike them. When all of these wavelengths are combined, we see white. On the other hand, when all of them are absorbed, and none reflected, we see black.

Color of transparent and translucent objects

• Only certain colors of light can pass through• The color of a transparent or translucent

object is the color of the light it transmits• Color filters

– Piece of glass or plastic that allows light of only a certain color to pass through it

– Ex: Red color filter only lets red light pass through– Ex: sunglasses –objects appear to change color

Copy these questions into your notebook!• Read pg 110 and 111 and answer:

– What are the primary colors of light?– What are 2 ways to make white light?– How do you make different colors of light?– What are the secondary colors of light?– What are complementary colors?– Answer question in figure 5.– What is a pigment?– How is mixing pigments of various colors different than mixing light of

various colors?– What are the primary colors of pigments?– What are the secondary colors of pigments?– Then, do section 1 assessment. You may work with partner.

DO NOW:

• What are the primary colors (in paint)?• How are they different from the primary

colors of light?

Combining Colors

• PRIMARY COLORS– 3 colors that can combine to make ANY other

color– RED, BLUE, GREEN

• SECONDARY COLORS– 2 primary colors mixed together – YELLOW, MAGENTA, CYAN

Primary + secondary color = WHITE light

Complementary colors

• Any two colors that combine to form white light– ex:

• Yellow and blue, • cyan and red, • Magenta and green

How does a color TV work?

• It uses only the primary colors of light (R, G, B) in different ratios/brightness to form all of the colors.

Mixing Pigments

•What is a pigment?

• Pigment = colored substances used to color other materials –found in ink, paints, dyes– They absorb some colors and reflect others– Whatever color a pigment reflects in the color

that you see!

What are the Primary colors of PIGMENTS?

Magenta, Cyan, Yellow

What happens when you keep adding pigments together?

• Fewer colors of light get reflected, so we see the mixture getting darker and darker

Section 2 – Reflection and Mirrors

Representing Light waves

• You can represent light waves as straight lines called RAYS.

What does “diffuse” mean?

• Ex: • John and Jack were in an argument about who

’s a better team—the Cubs or the White Sox. They started getting very angry at each other, and other students started getting involved…. so Mrs. P had to come in and diffuse the fight.

Regular Reflection vs. Diffuse Reflection

• Regular Reflection– Smooth surface, rays refelect all at the same angle

• Diffuse Reflection– Rough surface, rays reflect at different angles

How does your reflection wink?

• On a clean sheet of paper: • St. Cassian heading• Title: How does your reflection wink?• Procedure: Answer the two questions within

the procedure using COMPLETE sentences—restating the question.

• Observing: Answer the questions in complete sentences, restating the question.

PLANE MIRRORS• = an everyday mirror• A flat sheet of glass that has a smooth silver

colored coating on one side (normally the back)– Creates a regular reflection and clear image!

Image = copy of an object formed by reflected or refracted rays of light

DO NOW

• What does virtual mean?

Kind of Image in a Plane Mirror• You see a virtual image.

= an upright image that forms where light seems to come from. The image is the same size as the object, and it is reversed.

• Your image appears to be behind the mirror, but you cannot reach behind the mirror and touch it

• Even though the light rays are reflected, your brain treats them as if they had come from behind the mirror

When one looks into a mirror it appears as if you are looking through it and seeing the object on the other side.

Concave Mirrors• Parallel rays of light reflect so that they meet

at a point.• Focal point = point at which rays parallel to

the optical axis meet.

Representing How images form

• Use a ray diagram to see where focused image forms.

• See figure 10

• Concave mirrors can form either virtual images or real images• Virtual Image

– If object is between mirror and focal point– Appears behind the mirror and is upright– Always larger than object

• Real Image– When rays actually meet– It is upside down– Might be larger or smaller than object– Occurs when object is farther away from mirror than the focal

point

Convex Mirrors• Mirror with a surface that curves outward.

Convex Mirrors

• The rays appear to come from a focal point behind the mirror.

• The rays appear to come together but they never actually meet.

• The image formed will be virtual and smaller than the object.

• What is refraction?????????????

When light rays enter a medium at an angle, the change in speed causes the rays to bend, or change direction

Section 3 – Refraction and Lenses

• When you are looking at fish in a tank, what are the three mediums the light is passing through?

Water, glass, air

Refraction in Different Mediums

• Light bends more in some mediums than in others.

• When light passes – from airwater, it slows.– From water glass, it slows down more.– Glass air it ____________

• The glass causes the light to bend the most, so it has a high index of refraction.

• Index of refraction = measure of how much a ray of light bends when it enters the material– The higher the index, the more it bends light

Prisms and RainbowsPrisms and Rainbows

• When white light enters a prism, each wavelength of light is refracted by a different amount– Red has longest wavelength and is reflected least– Violet has shortest wavelength and is reflected

most– Same thing happens with water droplets in the

air.

Mirages• An image of a distant object caused by

refraction of light• See page 121.

DO NOW

• Where are places you see lenses everyday?• What do you know about lenses?

LensesLens = a curved piece of glass or other transparent material that is used to refract light

– It forms an image by refracting light rays that pass through it

– Type of image depends on• 1. shape of lens • 2. position of object

There are 2 types of Lenses

• 1. Convex• 2. Concave

• Make 2 columns and compare and contrast Convex and concave lenses.

Cow’s Eye Dissection-- Virtual

• http://www.exploratorium.edu/learning_studio/cow_eye/how.html

DO NOW

• What is needed to see? • What parts of the eye do you know already?

DO Now, cont’d

• Do Activity page 26. Answer the questions.

The Human Eye• You see objects when a process occurs that

involves both your eyes and your brain

1st. Light Enters the Eye

• 1.) Through the transparent cornea.– Protects eye and acts as lens to focus light rays

• 2.) Through the pupil– Black center of eye – an opening that becomes

larger to let in more light in the dark

IRIS

• Ring of muscle that contracts and expands to change the size of the pupil.

• Colored

2nd An Image Forms

• 1.) Light Passes through LENS– Convex– Refracts light to form image on lining of your

eyeball– Ciliary muscles hold lens in place.

An Image Forms, Cont’d• 2.) Ciliary muscles relax to focus on distant

objects, and contract to focus on nearby

An Image Forms, cont’d• 3. ) Upside-down image forms on retina

(layer of cells lining inside of eyeball)– a.) Rods

• Cells with a pigment that responds to low light. They help you see in dim light.

– B.) Cones• Cells that respond to color and respond best in

bright light

Rods and Cones

Third: A Signal Goes to the Brain

• Rods and cones send signals to the brain along a short, thick never called the optic nerve.

• It combines image from each of your eyes into a single 3D image.

Correcting Vision

• If your eyeball is slightly too long or too short, the image on retina is out of focus.

• Contacts and Glasses• Concave lenses correct nearsightedness.• Convex lenses to correct farsightedness

Nearsightedness

• Person can see nearby things clearly but faraway objects are blurred

• Need concave lens

Farsightedness

• Can see distant objects clearly, but nearby objects appear blurry

• Need convex lens

DO NOW

• Can you think of 3 common types of optical or light-using instruments ?

SECTION 5 – USING LIGHT

3 Common Optical Instruments

• 1. Telescope• 2. Microscope• 3. Camera

• What do you know about telescopes???

TELESCOPES

• Use lenses or mirrors to collect and focus light from distant objects

• Make distant objects look bigger

2 Types of Telescopes• 1. refracting

– Uses 2 lenses to focus light

• 2. reflecting– Uses a lens and a mirror to focus light

Microscopes

• What do you already know about microscopes?

Microscopes• Use a combination of lenses to focus light and

produce and magnify an image• Makes small, nearby images look bigger.

Camera• Uses a lens to focus light and form a real,

upside-down image on film in the back of the camera

• Forms images on film as “pictures”

5. Using Light