LightLight

Light:Light:

A type of energy that A type of energy that travels as a wavetravels as a wave

Rainbow colors:Rainbow colors:ROY G BIVROY G BIV– Red (longest wavelength)Red (longest wavelength)– OrangeOrange– YellowYellow– GreenGreen– BlueBlue– IndigoIndigo– Violet (shortest wavelength)Violet (shortest wavelength)

F. Y. I.F. Y. I.Light is different from other kinds of Light is different from other kinds of waves. It is part of the electromagnetic waves. It is part of the electromagnetic spectrum. Other kinds of waves, such spectrum. Other kinds of waves, such as sound waves must travel through as sound waves must travel through matter. Light waves do not need to matter. Light waves do not need to travel through matter. However, light travel through matter. However, light waves can go through matter, such as waves can go through matter, such as air, water, and glass.air, water, and glass.

White LightWhite Light

You get white light by You get white light by combining combining allall colors of colors of light!light!

You can get light that You can get light that appearsappears white by adding white by adding just three colors of light just three colors of light together: together: redred, , blueblue, and , and greengreen… … “The Primary “The Primary

Colors of Light”Colors of Light”

Combining colors of Combining colors of light is called light is called color color

addition.addition.

When two primary When two primary colors of light are added colors of light are added

together, you see together, you see secondary colorssecondary colors of of

light.light.

BlueBlue + + Green Green = = CyanCyan

BlueBlue + + RedRed = = MagentaMagenta

Red Red + + Green Green = = YellowYellow

Reflection:Reflection:

Happens when light Happens when light waves bounce off an waves bounce off an object (such as a object (such as a mirror or glass)mirror or glass)Where have you seen reflection?Where have you seen reflection?

Absorption Absorption When light is “soaked” in to a When light is “soaked” in to a substance. When all colors are substance. When all colors are absorbed, we see black. When all absorbed, we see black. When all colors are reflected we see white. colors are reflected we see white. Combinations of reflection and Combinations of reflection and absorption give us the different colors absorption give us the different colors we see. For example: A green shirt, we see. For example: A green shirt, reflects green, but absorbs red.reflects green, but absorbs red.

What’s going on?What’s going on?Imagine you and a friend are at Imagine you and a friend are at a lake. Your friend wades into a lake. Your friend wades into the water. You look at her, and the water. You look at her, and her feet appear to have her feet appear to have separated from her legs!!! You separated from her legs!!! You know her feet did not fall off. know her feet did not fall off. How do you explain this? It How do you explain this? It has to do with refraction!has to do with refraction!

Refraction:Refraction:

The bending of a wave The bending of a wave as it passes at an angle as it passes at an angle from one substance, or from one substance, or type of matter, to type of matter, to anotheranother

Answer:Answer:In the case of your friend In the case of your friend and her “detached” feet, and her “detached” feet, the light wave was bent as the light wave was bent as it passed from the air (a it passed from the air (a gas) to the water (a gas) to the water (a liquid). Whew!!!liquid). Whew!!!

F. Y. I.F. Y. I.White light is composed of all the White light is composed of all the wavelengths of visible light. Humans see wavelengths of visible light. Humans see the different wavelengths as different the different wavelengths as different colors. White light can be separated into colors. White light can be separated into different colors during refraction. Color different colors during refraction. Color separation by refraction is responsible for separation by refraction is responsible for the formation of rainbows. Rainbows are the formation of rainbows. Rainbows are created when sunlight is refracted by water created when sunlight is refracted by water droplets!droplets!

Transparency #293Transparency #293

Prisms produce rainbows Prisms produce rainbows through refraction. Light passing through refraction. Light passing

through a prism is refracted through a prism is refracted twice – once when it enters and twice – once when it enters and

once when it leaves.once when it leaves.

Diffraction:Diffraction:

The bending of The bending of waves around waves around barriers or through barriers or through openingsopenings

F. Y. I.F. Y. I.The wavelength of light is very small (100 The wavelength of light is very small (100 times thinner than a human hair). times thinner than a human hair).

Since light waves are so thin, they cannot Since light waves are so thin, they cannot diffract very much around large obstacles. diffract very much around large obstacles. Thus, you cannot see around corners. Thus, you cannot see around corners.

You can observe light waves diffracting if You can observe light waves diffracting if you examine the edges of a shadow. you examine the edges of a shadow. Diffraction causes the edges of a shadow Diffraction causes the edges of a shadow to be blurry. to be blurry.

Transparent:Transparent:Matter through which Matter through which light is easily light is easily transmitted transmitted Examples: air, glass, Examples: air, glass, plastic wrap, and waterplastic wrap, and water

Translucent:Translucent:

Matter that transmits Matter that transmits light but also scatters light but also scatters the light as it passes the light as it passes through the matterthrough the matter

Example: wax paperExample: wax paper

Opaque:Opaque:Matter that does not Matter that does not transmit any lighttransmit any light

Example: metal, wood, Example: metal, wood, and aluminum foiland aluminum foil

Material that absorbs Material that absorbs light is opaquelight is opaque

Question:Question:

Why is the sky Why is the sky blueblue??

Answer:Answer:As light moves through the atmosphere, As light moves through the atmosphere, most of the longer wavelengths, such as most of the longer wavelengths, such as redred, , orangeorange, and , and yellowyellow pass straight pass straight through.through.However, much of the shorter wavelength However, much of the shorter wavelength light is absorbed by the gas molecules in the light is absorbed by the gas molecules in the air. The absorbed air. The absorbed blueblue light is then radiated light is then radiated in different directions. It gets scattered all in different directions. It gets scattered all around the sky. Whichever direction you around the sky. Whichever direction you look, some of this scattered look, some of this scattered blueblue light light reaches you. Since you see the reaches you. Since you see the blueblue light light from everywhere overhead, the sky looks from everywhere overhead, the sky looks blueblue. .

ScatteringScattering explains why explains why light becomes weaker with light becomes weaker with distance. distance. Blue Blue has a very has a very

short wavelength and short wavelength and scatters more than any scatters more than any

other color.other color.

Question:Question:

If If violetviolet has the has the shortest wavelength, shortest wavelength, why isn’t the sky why isn’t the sky violetviolet??

Answer:Answer:There are two reasons why There are two reasons why the sky is not the sky is not violetviolet!!

1. There is not enough 1. There is not enough violetviolet in visible light. in visible light.

2. The wavelength is too 2. The wavelength is too short.short.