Warm Up

• 1. Draw the EM spectrum. • 2. Draw and label a transverse

wave. • 3. Draw a high frequency wave. • 4. What are the different types of

energy?• 5. What are the 6 characteristics of

life?

Let there be LIGHT

Light • Light travels in straight lines at a speed of

186,000 miles per second or 3.0 X 10^8 m/s.

• *Light waves travel faster than sound waves!

• (Light energy from the sun travels through space , reaches earth, and some of it turns to heat energy and warms the earth’s air.)

• *When light reaches an object, it is absorbed, reflected, or passes through it.

Part 1 – Properties of Light

•Light travels in straight lines:

Laser

• We see things because they reflect light into our eyes:

Homework

“Just Passing Through:” What happens when light strikes glass? Or waxed paper? Or a book?

• If light is blocked by an object and a dark shadow is cast it is = opaque.

• If some light passes through but not all and a light shadow is present it is = translucent.

• If light travels through an object it is = transparent

What happens when light hits these objects?

• Glass of water • School bus

window• Notebook paper• Waxed paper• Plastic wrap• Tissue paper• Cardboard• Textbook• Hand lens…

Transparent objects:

• The windows on a school bus,• A clear empty glass,• A clear window pane,• The lenses of some eyeglasses,• Clear plastic wrap,• The glass on a clock,• A hand lens,• Colored glass…• ALL of these are transparent.

Yes, we can see through them because light passes through each of them.

Translucent objects• Thin tissue paper,• Waxed paper,• Tinted car windows,• Frosted glass,• Clouds,• All of these

materials are translucent and allow some light to pass but the light cannot be clearly seen through.

Opaque objects:• Heavy weight paper,• Cardboard• Aluminum foil,• Mirror, bricks, buildings,• Your eyelids and hands,• Solid wood door,• All of these objects are

opaque because light cannot pass through them at all.

• They cast a dark shadow.

Warm Up• 1. What happens when light is

diffracted?• 2. What happens when light is

refracted?• 3. Draw and label the EM

spectrum. • 4. What does it mean if something

is translucent?• 5. What is the law of reflection?

Part 2 - Reflection• Reflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of Reflection

Mirror

Angle of Incidence

•The Law of ReflectionThe Law of Reflection

Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection

In other words, light gets reflected from a surface at the same angle it hits it.

The same !

!!

Clear vs. Diffuse Reflection

• Smooth, shiny surfaces have a clear reflection:

Rough, dull surfaces have a diffuse reflection.

Diffuse reflection is when light is scattered in different directions

Refraction

• Light BENDS because it changes speed as it goes through different mediums. IE: water

Warm Up

• 1. Draw and label EM spectrum. • 2. Give an example for each of the

waves on the EM spectrum.

Refraction

Scattering

• When light is scattered on an object smaller than the wavelength of light, the process is called scattering

• The color of the sky is the direct result of scattering of the sunlight.

Diffraction

*** bending around an object / cor- ners***

•Diffraction is the slight bending of light as it passes around the edge of an object.

• If the opening is much larger than the light's wavelength, the bending will be almost unnoticeable.

• However, if the two are closer in size or equal, the amount of bending is considerable, and easily seen with the naked eye.

Draw

Orange

RedWhite Light

Yellow

Green

Blue

Indigo

Violet

ColorObjects have color because they reflect certain wavelengths of light.

Objects appear red because they absorb all colors except red which is reflected.

Objects which are green appear so because they absorb all colors except green which is reflected.

Colors of light are additive. Mixing colors of light results in white light – all colors reflected.

Pigments subtract color by absorbing wavelengths of light. Mixing pigments results in all colors being absorbed and no colors being reflected - black

Refraction of light – The bending of light as it passes from one medium to another.

Refraction make objects appear to be in different positions.

Refraction in the atmosphere creates mirages

Light can be refracted at the boundary between two transparent mediums.

Fiber optics use total internal reflection.

Prisms bend each color of light at a different angle because the higher the frequency, the more it is refracted

How do we see different colors?

• Black?• Absorbs ALL the color energy frequencies of

visible light• White?

• Reflects ALL the color energy frequencies of visible light

• Grey?• Absorbs and reflects = percentages of all the

colors• Other colors?

• Reflects the color(s) you see and absorbs all others