Electromagnetic Waves

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Electromagnetic Waves

• Electromagnetic waves dont 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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Radio Waves

• Arecibo Observatory Puerto Rico - the site of
  the world's largest single-dish radio telescope
• VLA Research Center
• 27 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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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

• Light from the Sun is white light composed of
  different wavelengths which we see as different
  colors
• When all colors or Primary colors(R,G,B) are
  combined, we see white light
• Visible light is NOT dangerous

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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 producing ultraviolet light which
  excites 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.
  Light of the future!

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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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X-Ray

• Properties Very high Frequency, short
  wavelength with very high energy capable of
  penetrating living tissue and causing burns or
  Cancer
• Emitted by
• Astronomical objects
• X-ray machines medical, dental, security
• CAT scan machines(MRI is not x-ray)
• Older televisions
• Radioactive minerals

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Gamma RaysVery 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 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

• Rodsreact 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 ways
• Reflected - light rays reflect at angle of
  incidence
• Absorbed - energy is transferred to the
  particles
• Transmitted light passing through the matter
• Refracted light bending from matter to another
• TYPES OF MATTER
• Transparent - 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 (exceptionsNCIS,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
• DoC FltDoltC DoltF
  rdcmc.gif http//www.csupomona.edu/bmho
  eling/ReflectionMirrors/ReflectionMirrors8.html
• Inverted Inverted
  Upright
• Same Enlarged
  Enlarged
• Real Real Virtual

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Do gt C
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Convex Mirror

• Virtual, upright, diminished
• http//www.edumedia-sciences.com/en
  /a309-convex-mirror
• Use this diagram and the animation above, NOT the
  one in the book

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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.act
ion?quick99att658
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Convex Lens Ray Diagrams

• Do gt F C
• Inverted, Real
• Diminished
• C ltDogt F
• Inverted, Real
• Enlarged
• Do lt F Upright, Virtual,Enlarged
• See Page 579
• http//www.absorblearning.com/media/attachment.act
  ion?quick163att3019
• http//www.youtube.com/watch?vHGVUVFcyc6o

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Sound
Light
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Sound
Light
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
Travel in waves Possess energy Frequency Can
reflect Can be damaging
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Light Websites

• Molecular Expressions http//micro.magnet.fsu.ed
  u/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/teacher
  slab/science/light/index.html
• Physics of Light and Color http//www.olympusmic
  ro.com/primer/lightandcolor/index.html
• Mixing Colors of LIGHT http//mc2.cchem.berkeley
  .edu/Java/RGB/example1.html