Warm Up 6.2List the colors of the visible light

spectrumWhich color has the longest wavelengthWhich color has the most energy? (hint:

shorter wavelengths have the most energy)

Light

How light waves interact with materials Light can be reflected, transmitted, or

absorbed.

Materials can be classified according to the amount and type of light they transmit

Transparent-

Transparent Materials allow most of the light that strikes them to pass through

Examples:windows, light bulbs, clock

faces, ziploc bags

Translucent-

Translucent▪ Materials transmit some light, but they also cause it to spread out in all directions

Examples: lampshades, sheer fabrics,

frosted glass

Opaque- Opaque

▪ Materials do not allow any light to pass through them because they reflect light, absorb light, or both.

Examples:

heavy fabrics, wood, rocks, construction paper

Visible Light

Part of the EM spectrum we can seeRed, Orange, Yellow, Green, Blue,

Indigo, & Violet (ROY G BIV) Red has the longest wavelength Violet has the most energy

What determines color of an object?2 factors determine the color of an

object1. The wavelengths that the object itself

reflects or absorbs2. The wavelengths present in the light that

shines on the object

Color Reflection & Absorption

Reflection

Absorption

White Color

Black Color

Wavelengths that an object bounces back and are seen

Wavelengths that are absorbed and not seen

Is seen when all the wavelengths are reflected

Is seen when all the wavelengths are absorbed

Wavelengths Present Ex: If you only

shine red light on a white piece of paper, the paper will appear red, not white-

Red light is the only light that is available to be reflected

Primary Colors of Light vs.

Primary PigmentsPRIMARY COLORS OF LIGHT The human eye can

only detect- red, green & blue. When all 3 are mixed

together equally they make white light

PRIMARY PIGMENTS Cyan, yellow, &

magenta are the primary pigments When all 3 are mixed

together, they make black

ReflectionWe describe the path of light as

straight-line raysReflection off a flat surface follows

a simple rule: angle in (incidence) equals angle out

(reflection) angles measured from surface

“normal” (perpendicular)

surface normal

sameangle

incident ray exit ray reflected ray

Reflection VocabularyReal Image –

Image is made from “real” light rays that converge at a real focal point so the image is REAL

Can be projected onto a screen because light actually passes through the point where the image appears

Always inverted

Reflection Vocabulary

Virtual Image– “Not Real” because it cannot be projected

Image only seems to be there!

PLANE MIRRORFlat Mirror ex: Hall Mirror

Useful to think in terms of images

“image” you

“real” you

mirror onlyneeds to be half as

high as you are tall. Yourimage will be twice as far from you

as the mirror.

PLANE MIRRORLEFT- RIGHT REVERSAL

AMBULANCE

Curved mirrorsWhat if the mirror isn’t flat?

light still follows the same rules, with local surface normal

Parabolic mirrors have exact focus used in telescopes, backyard satellite

dishes, etc. also forms virtual image

Concave Mirrors▪Curves inward▪May be real or virtual image

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Convex Mirrors

▪Curves outward▪Reduces images▪Virtual images

Use: Rear view mirrors, store security…

CAUTION! Objects are closer than they appear!

RefractionRate at which material slows down speed

of lightThe “light slowing factor” is called the

index of refraction glass has n = 1.52, meaning that light travels

about 1.5 times slower in glass than in vacuum

water has n = 1.33 air has n = 1.00028 vacuum is n = 1.00000 (speed of light at full

capacity)

Convex Lenses

Thicker in the center than edges. Lens that converges

(brings together) light rays.

Forms real images and virtual images depending on position of the object

The Magnifier

Concave Lenses

Lenses that are thicker at the edges and thinner in the center. Diverges light

rays All images are

erect and reduced.

The De-Magnifier

How You See

Near Sighted – Eyeball is too long and image focuses in front of the retina

▪ Near Sightedness – Concave lenses expand focal length

Far Sighted – Eyeball is too short so image is focused behind the retina.

▪ Far Sightedness – Convex lens shortens the focal length.

Mirror Mini-LabHold the convex mirror arm length

away and record your observations as you move it slowly towards your face.

Ex: Are you Big or Small? Fuzzy or clear? Right side up or Upside Down?

Does any thing change as you move it closer?

Repeat using the concave mirror.