RESA Electromagnetic Waves Electromagnetic waves don’t need a medium Gamma, X-rays, Ultraviolet, Visible, Infrared, Microwaves(radar), Radio, TV Travel.

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Electromagnetic Waves

• Electromagnetic waves don’t need a medium

• Gamma, X-rays, Ultraviolet, Visible, Infrared, Microwaves(radar), Radio, TV

• Travel at 300,000,000m/s (186,000miles/sec)

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Microwaves (Radar) Waves

• Radar waves detect objects at a distance by reflection like Sonar in water

• Microwave ovens use electromagnetic waves to energize water molecules into motion and friction causes temperature increase

• Should not put metal in path of microwaves

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Radio(AM & FM), TV, Cell phone Waves

• Very long wavelength

• Very low frequency

• Very low energy content

• Can pass through most buildings but stopped by thick concrete

• Do not seem to be harmful

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Infrared Frequency

• Frequency less than Visible• Certain animals (like snakes)

can "see" infrared light.• This allows them to find warm

blooded prey in the dark because thermal energy is emitted in the infrared.

• Scientists have developed cameras that allow us to "see" infrared light (Heat leaking).

• "False colors" have been used to indicate temperature.

• http://son.nasa.gov/tass/images/cont_emspec2.jpg

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Infrared photography

• These images of the Earth showing ocean temperatures were taken from a satellite. Global warming is visible.

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Visible Light• We see different wavelengths as different

colors

• When all colors are combined, we see white light

• When there are no colors, we see black

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All visible Light production

• Electrons live in a “ground state” where the energy is the lowest

• If an outside source of energy is supplied, electrons can “Jump” to higher, empty energy levels

• When the energy source ends, the electrons fall back to “ground state” and release the extra energy as LIGHT

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Visible Light production • Incandescent: Electricity is passed thru a wire with

high resistance (Tungsten). Resistance produces heat and a little light. Low efficiency.

• Fluorescent: Electricity is passed thru a low pressure gas (Hg Vapor). The gas and a powder coating glow. These include CFL bulbs. More efficient than incandescent.

• Neon: Same as above but gas is Noble gas• Halogen: small filament and Halogen gas(headlights)• LED: Light emitting diode allowing electrons to fill

holes in metal surfaces. Very efficient.

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Ultraviolet Frequencies

• Higher frequency, shorter wavelength than visible• High energy can cause “sun” burn and Cancer• Bees are able to see “ultraviolet”

• Milky way – visible light vs. ultraviolet telescope

http://son.nasa.gov/tass/images/cont_emspec2.jpg

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Radio Waves

• Arecibo Observatory – Puerto Rico - the site of the world's largest single-dish radio telescope

• VLA Research Center27 large radio telescopes in New Mexico researching outer space. They have discovered things like rings on other planets and planets outside of the Solar System.

http://www.naic.edu/

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X-Ray• Properties – Very high Frequency, short wavelength

with very high energy capable of penetrating living tissue

• Emitted by– Astronomical objects – X-ray machines– CAT scan machines– Older televisions– Radioactive minerals– Airport luggage scanners

• Detected by– Space based X-ray detectors– X-ray film

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Gamma Rays—Very Dangerous• Properties – Highest frequency, shortest

wavelength and HIGHEST ENERGY. Can cause much damage in living tissue.

• Emitted by– Radioactive materials– Exploding nuclear weapons– Gamma-ray bursts from outer space– Solar flares,Pulsars, Supernovae, Black Holes

• Detected by– Gamma detectors and astronomical satellites– Medical imaging detectors

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What is LIGHT? PHOTONS!

• A type of electromagnetic waveelectromagnetic wave• Energy travels as a particle which includes a wave• Transverse Wave in little packets called PHOTONS• Photons contain different wavelength (colors)• NO medium is required• We see things because of one of two reasons

– 1. They actually produce their own light(Sun)– 2. They reflect light off of their surface(Moon)

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Apple in the Dark

• Keely, Page. Uncovering Student Ideas in Science. Vol 1

• Answer: “The best response is A. In order to see an object, light must be emitted from or reflected off an object so that it reaches the eye. It is impossible to see in the absence of light (total darkness).”

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The Human Eye• Eyeball Diagram• Pupil does not

exist!• Iris is the color• Lens is focused by

ciliary muscles• Eye is moved by

muscles• Retina contains the

Rods and Cones

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How the Eye Sees• Light enters through the cornea which helps to

focus the light.• The clear, watery fluid behind the cornea is the

aqueous humor which keeps a constant pressure within the eye.

• Light next passes through the iris which is the colored part of the eye.

• Light then enters the pupil – hole which looks like a black dot in the middle of the eye.

• Light next goes through the lens. Which focuses the light. The lens changes shape to focus on light reflecting from near or distant objects.

• This focused light now beams through the center of the eye. Surrounding the vitreous is the tough, fibrous, white part of the eye known as the sclera.

• Light reaches its final destination: the retina located at the back of the eye.

http://www.webmd.com/eye-health/amazing-human-eye

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How the Eye Sees• The focused light is projected onto the

flat, smooth surface of the Retina. • The retina has many parts including the

macula, blood vessels & photoreceptors.

• Photoreceptors (Rods and Cones) are specialized nerve endings that convert the light into electro-chemical signals. These signals travel to the Optic nerve which carries all the information collected from the eye to the brain.

• Light has reflected from an object, entered the eye, been focused, and converted into electro-chemical nerve signals. The brain then must receive -- and interpret -- the eye's signals. Once this is done, vision occurs.

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Rods and cones

• Rods—react to small amounts of light– black, white & shades of gray

• Cones– respond to colors in bright light. Different cones respond to each color of light

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Near and Far Sightedness• Near(clear) sightedness• The lens focuses the light rays

before they contact the retina. Correction uses a diverging lens(concave).

• Far (clear) sightedness• The lens focuses the light ray

after they contact the retina.• Correction uses a converging

lens(convex).

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Astigmatism

• Blurred vision caused by a lens that is not symmetrical.

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LIGHT Hitting a Surface

• Light can interact with matter in 4 ways1. Reflected - light rays reflect at angle of incidence

2. Absorbed - energy is transferred to the particles

3. Transmitted – light passing through the matter

4. Refracted – light bending from matter to another

• TYPES OF MATTER– TransparentTransparent - light is easily transmitted– Translucent - transmits and scatters light– Opaque - does not transmit any light

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Seeing COLORROY G BIV

• Human eyes have both light and color receptors called rods and cones (most mammals have only light receptors

• It is because visible light has color that we see objects as having different colors

• Grass appears green because grass reflects only green light and absorbs all other colors

• Our visual system perceives different wavelengths of light as different colors

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COLORS of OBJECTS

• The color of an object is determined by the wavelength of color that reaches your eye.

• OPAQUE OBJECTS– When white light hits a colored object, some colors

are absorbed and some are reflected– Only the light that is reflected reaches your eyes, this

is the color that we see• White objects REFLECT ALL colors• Black objects ABSORB ALL colors

• TRANSPARENT OBJECTS– We see the color that is transmitted through the

matter

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Mixing COLORS of Light• RED, BLUE and GREEN can be combined in

different ratios to produce colors of visible light– Called the Primary Colors– When they are mixed, they make secondary colors

Mixing COLORS of Pigment– Pigment - material that gives a substance color by

absorbing colors of light and reflecting others– Primary pigments – Cyan, Yellow & Magenta– This is why we cannot mix red, blue and green

paint to make white paint. Instead it is black. Why?

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Law of Reflection• Law states that:

– angle of incidence = angle of reflection– Angle of Light going into surface = angle going out

If the reflecting surface is smooth, then light reflects off of all points at the same angle (MIRROR).

If the reflecting surface is rough (MOON), then light reflects off at many different angles(Diffusion).

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Mirrors Reflect Light

Mirrors are classified by their shape,

– Plane– Concave– Convex

• The shape of the mirror affects the way light REFLECTS from it and how an image appears

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Plane Mirrors

• A mirror with a flat surface• When you look at it, your reflection is upright

and the same size as you are• Images are reversed from left to right• Image appears to be the same distance from the

mirror as in front of it• Most mirrors are opaque, light does NOT travel

through them (exceptions:NCIS,CIS, Police)• The image created is virtual-your brain sees

the reflected light and thinks it is straight behind the mirror & cannot be projected.

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Focal Point

• Concave

• Mirror

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Images for Concave Mirrors

C is always two times focal length Do=C F<Do<C Do<F

rdcmc.gif http://www.csupomona.edu/~bmhoeling/ReflectionMirrors/ReflectionMirrors8.html

Inverted Inverted Upright

Same Enlarged Enlarged

Real Real Virtual

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Do > C

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Convex Mirror• Virtual, upright, diminished • http://www.edumedia-sciences.com/en/a309-convex-mirror

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Refraction• The direction of light can be changed at the

boundary of two media having different densities because of speed change of the light.

http://csep10.phys.utk.edu/astr162/lect/light/ref-diff.html

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Lenses Refract Light

• Lens - a curved, transparent object that forms an image by refracting, or bending light

• Classified by shape– Convex - thicker in the middle than at the

edges. Bending rays toward the middle- Converging the rays.

– Concave - Thinner in the middle than at the edges. Bending rays toward the outer edges Diverging the rays.

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Convex Lenses are Converging

• Focal point(F) is where all rays converge

• Center of curvature(C) is always 2xF

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Concave Lenses are Diverging

• Image can only be virtual

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Image from a Concave Lens

• Image is Upright, Diminished and Virtual

http://www.absorblearning.com/media/attachment.action?quick=99&att=658

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Convex Lens Ray Diagrams

• Do > F & C– Inverted, Real– Diminished

• C <Do> F– Inverted, Real– Enlarged

• Do < F Upright, Virtual,Enlarged• See Page 579

• http://www.absorblearning.com/media/attachment.action?quick=163&att=3019• http://www.youtube.com/watch?v=HGVUVFcyc6o

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Travel in waves

Possess energy

Frequency

Can reflect

Can be damaging

Mechanical wave

Longitudinal

Needs a medium to propagate

Pitch

Echo

Measured in decibels

Thunder

Diffraction

Electromagnetic

Transverse

Can travel though Vacuum

Color

Mirror reflection

Measured in lumens

Lightning

Refraction

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Light Websites

• Molecular Expressions: http://micro.magnet.fsu.edu/optics/activities/students/index.html

• Learning Center Lab: http://micro.magnet.fsu.edu/optics/activities/students/properties.html

• Teacher Light Lab: http://www.learner.org/teacherslab/science/light/index.html

• Physics of Light and Color: http://www.olympusmicro.com/primer/lightandcolor/index.html

• Mixing Colors of LIGHT: http://mc2.cchem.berkeley.edu/Java/RGB/example1.html