LIGHT

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LIGHT the Electromagnetic Spectrum
Examining Light 2008
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• We will investigate the following
• 1. What is light?
• 2.What are some sources of light around us?
• 3. What are opaque, transparent, translucent
• objects?
• 4. What is a light wave?

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Light

• Our primary source of light is the sun.
• Light travels in straight lines at a speed of
  186,000miles per second.
• 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 earths air.
• Light from the sun also travels to the cells of
  green plants (producers) and is stored as energy.
• When light reaches an object, it is absorbed,
  reflected, or passes through it.

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Sensing Light

• Humans have two light detectors.
• Do you know what they are called?

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How many sources of Light can you list and
explain?

• SUNwarms air,
• water, and land.
• Fireprovides heat, light, and cooking fuel.
• Lightning
• Firefly
• Flashlight
• Light bulb
• Laser beams
• Optical
• telephone
• fibers
• Traffic lights

AIMS Primarily Physics Light Sources Activity
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Just Passing Through What happens when light
strikes glass? Or waxed paper? Or a book?

• If light travels through an object it is
  transparent
• 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 istranslucent.

AIMSPrimarily Physics Just Passing Through
Activity
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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

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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.

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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.

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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.

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What is light really?Electromagnetic radiation
waves

• Light waves are three dimensional.
• Light waves vibrate in all planes around a center
  line.
• The waves have high points called crests.
• Waves also have low points called troughs.
• The distance from one crest to the next crest is
  called a wavelength.
• The number of waves passing a given point in one
  second is called the frequency.

wavelength
A Science Museum of VA Light Science Activity
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Notice the wavelength is long(Radio waves) and
gets shorter (Gamma Rays)
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Electromagnetic Radiation

• Electromagnetic radiation can be described as a
  stream of photons. Each photon traveling in a
  wave-like pattern, moving at the speed of light
  and carrying some amount of energy.
• The only difference amongst radio waves, visible
  light, and gamma-rays is the amount of energy of
  the photons. Radio waves have photons with low
  energies. Microwaves have a little more energy
  than radio waves. Gamma-rays and cosmic rays
  have highest energy waves and are the deadliest.

Page info from NSTA Conference 2004
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Dont forgetlongest waves (radio) ..to shortest
waves (cosmic)
Page info from NSAT Conference 2004
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Science Museum of Virginia Acting It Out!
Activity Scaling the Spectrum Activity OR GEMS
Invisible Universe Comparing Wave Makers I.
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Radio(Longest electromagnetic waves)

• Emitted by
• Astronomical Objects
• Radio Station Transmitters
• Detected by
• Ground based radio telescopes
• If you turn on a radio,, it will convert the
  radio wave energy into sound energy.

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Television

• Shorter than radio, also used to carry messages
  (pictures sound) to our TV sets.
• We can sense the TV waves around us with our
  televisions.

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Microwave

• Emitted by
• Gas clouds collapsing into stars
• Microwave Ovens
• Radar Stations
• Cell Phones
• Detected by
• Microwave Telescopes
• Food (heated)
• Cell phones
• Radar (systems)

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Infrared(Heat or Thermal)Are you a source of
infrared? YES you are!

• Emitted by
• Sun and stars (Near)
• TV Remote Controls
• Food Warming Lights (Thermal)
• Everything at room temperature or above,HEAT
• Detected by
• Infrared Cameras
• TVs, VCRs,
• Your skin

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Lets take a look at Herschels Experiment

• Herschels Experiment
• Discovered Invisible Light
• In 1800, Herschel places his control thermometer
  just outside the red end of the spectrum
• Result The outside thermometer registered the
  highest temperature

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Lets set up Herschels Experiment

• Set up of Box Design for Conducting the Herschel
  Experiment.

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Conducting Hershels Experiment

• Place a sheet of white paper inside a cardboard
  box
• Tape three thermometers together and place inside
  box
• Cut a small notch in the top of the box and
  position a glass prism so that the spectrum is
  projected inside the box
• Arrange the thermometers so that one is just
  outside the red end of the spectrum, with no
  visible light falling on it

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VisibleEach color is a different size wave.Red
the longest violet the shortest

• Emitted by
• The sun and other astronomical objects
• Laser pointers
• Light bulbs
• Detected by
• Cameras
• (film or digital)
• Human eyes
• Plants (red light)
• Telescopes

RoyG.Biv
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Color

• White light is not a single color it is made up
  of a mixture of the seven colors of the rainbow.

We can demonstrate this by splitting white light
with a prism This is how rainbows are formed
sunlight is split up by raindrops.
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The colors of the rainbow

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

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Adding colors

• White light can be split up to make separate
  colors. These colours can be added together
  again.
• The primary colors of light are red, blue and
  green

Adding blue and red makes magenta (purple)
Adding blue and green makes cyan (light blue)
Adding all three makes white again
Adding red and green makes yellow
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Seeing color

• The colour an object appears depends on the
  colours of light it reflects.

For example, a red book only reflects red light
White light
Only red light is reflected
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A pair of purple trousers would reflect purple
light (and red and blue, as purple is made up
of red and blue)
Purple light
A white hat would reflect all seven colours
White light
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Using colored light

• If we look at a colored object in coloured light
  we see something different. For example,
  consider a football kit

Shirt looks red
White light
Shorts look blue
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• In different colors of light this kit would look
  different

Red light
Shirt looks red
Shorts look black
Shirt looks black
Blue light
Shorts look blue
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Some further examples
Object Colour of light Colour object seems to be
Red socks Red Red
Red socks Blue Black
Red socks Green Black
Blue teddy Red Black
Blue teddy Blue
Blue teddy Green
Green camel Red
Green camel Blue
Green camel Green
Magenta book Red
Magenta book Blue
Magenta book Green
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Using filters

• Filters can be used to block out different
  colors of light

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Investigating filters
Colour of filter Colours that could be seen
Red
Green
Blue
Cyan
Magenta
Yellow
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Red
White
Blue
Green
Magenta
Yellow
Cyan
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UltravioletSunburn / black light
He can get skin cancer!

• Emitted by
• Tanning booths (A)
• The sun (A)
• Black light bulbs (B)
• UV lamps
• Detected by
• Space based UV detectors
• UV Cameras
• Flying insects (flies)

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X-ray

• 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
• CCD detectors

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Chandra X-ray Observatory

• Chandra is designed to observe X-rays from high
  energy regions of the universe, such as the
  remnants of exploded stars.
• The most sophisticated observatory built to date.
• Deployed by the Space Shuttle Columbia on July
  23, 1999,

Chandra X-ray Observatory
Slide from 2004 NSTA Conference
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Gamma Ray(Short electromagnetic waves but more
energetic)

• Emitted by
• Radioactive materials
• Exploding nuclear weapons
• Gamma-ray bursts
• Solar flares
• Detected by
• --Geiger counters
• Gamma detectors and astronomical satellites
• Medical imaging detectors

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Sources of g-ray Emission

• Black holes
• Active Galaxies
• Pulsars
• Diffuse emission
• Supernovae
• Gamma-ray bursts
• Unidentified

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COSMIC Rays(The highest energy waves and the
deadliest)

• Cosmic rays come from deep space and can pass
  through the Earth.

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How big are the waves?

• A great question!
• Radio waves (Buildings to
• human size)
• Microwaves
• (Humans-beetles)
• Infrared waves
• (Eye of a needle)
• Visible waves
• (microscopic size)!
• WOW! All the rest are the size of molecules,
  atoms, atomic nuclei and smaller..

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or
Snells Law !
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Reflection

• Reflection from a mirror

Normal
Reflected ray
Incident ray
Angle of reflection
Angle of incidence
Mirror
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• The Law of Reflection

Angle of incidence Angle of reflection
In other words, light gets reflected from a
surface at ____ _____ angle it hits it.
The same !!!
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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
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Using mirrors

• Two examples

2) A car headlight
1) A periscope
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Refraction

• Light bends towards
• the normal in a denser material

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Refraction happens because the light slows down
in the material
(the part of the beam that arrives first slows
down first)
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Glass
Air
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You can experiment with effects of different
incident angles and refractive indices with
Figure 3. You can move the flashlight around, and
change the refractive index of the top and bottom
mediums. You can use the buttons to quickly enter
the index for a few common mediums. Critical
Angle Using the refraction simulator, notice how
the light bends toward the normal when the light
enters a medium of greater refractive index, and
away from the normal when entering a medium of
lesser refractive index. Then notice what happens
when you move the flashlight to an angle close to
90 or -90 degrees in the medium with a higher
refractive index. As you approach the critical
angle the refracted light approaches 90 or -90
degrees and, at the critical angle, the angle of
refractions becomes 90 or -90 and the light is no
longer transmitted across the medium/medium
interface. For angles greater in absolute value
than the critical angle, all the light is
reflected. This is called total reflection.