Transcript LIGHT: What is it? - Gallaudet University

WAVES:
LIGHT moving
Waves carry energy from
one place to another
The NATURE of WAVES
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Waves – A wave is a disturbance that
transfers energy.
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A medium – A substance which transmits a
wave.
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Speed of waves – depends on the properties
of the medium.
This drawing shows
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1. reflected energy
2. transmitted energy
3. emitted energy
4. absorbed energy
This drawing shows
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1. reflected energy
2. transmitted energy
3. emitted energy
4. absorbed energy
This drawing shows
1. reflected energy
 2. transmitted energy
 3. emitted energy
 4. absorbed energy
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This drawing shows
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1. reflected energy
2. transmitted energy
3. emitted energy
4. absorbed energy
Light &
the Electromagnetic Spectrum
LIGHT: What Is It?
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Light Energy
 Atoms
 As atoms absorb energy, electrons jump out
to a higher energy level.
 Electrons release light when falling down to
the lower energy level.
 Photons - bundles/packets of energy released
when the electrons fall.
Light: a stream of Photons
Electromagnetic Waves
 Speed
in Vacuum
 300,000 km/sec
 186,000 mi/sec
 Speed in Other Materials
 Light is slower in Air, Water, Glass
Transverse Waves
 Energy
is perpendicular to direction of
motion
 Moving photon creates electric &
magnetic field
 Light has BOTH Electric & Magnetic
fields at right angles!
Electromagnetic Spectrum
Electromagnetic Spectrum
Radio Waves
Longest wavelength & lowest
frequency.
Size of a football field +
Radio & T.V. broadcasting.
Electromagnetic Spectrum
 Microwaves
 About the size of a
baseball
 Used in radar,
cooking, pagers,
cells
Electromagnetic Spectrum
Infrared Rays
 Light rays with longer
wavelength than red light.
 Longer IR is heat
 Cooking, Medicine, T.V.
remote controls
Which is the same thing as heat?
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1. Visible light
2. Infrared light
3. Radio waves
4. Ultraviolet radiation
This drawing shows
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1. convection
2. transmitted energy
3. conduction
4. absorbed energy
This drawing shows
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1. convection
2. transmitted energy
3. conduction
4. absorbed energy
LandSat satellite
Electromagnetic Spectrum
Spectrum – Light we can see
 Roy G. Biv – Acronym for Red,
Orange, Yellow, Green, Blue, Indigo,
& Violet.
 Largest to Smallest Wavelength.
 Visible
Electromagnetic Spectrum
Ultraviolet rays.
EM waves slightly shorter than
visible light
Used in food processing & hospitals
to kill germs’ cells
Helps your body use vitamin D.
Electromagnetic Spectrum
 X-Rays
are shorter than UV rays.
 Medicine – Bones absorb x-rays;
soft tissue does not.
 Lead absorbs X-rays.
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Electromagnetic Spectrum
 Gamma
rays
 Shortest wavelength EM waves.
They come from outer space.
Uses: cancer treatment.
The Atmosphere absorbs wavelengths
LIGHT: Particles or Waves?
 Wave
Model of Light
 Explains most properties of light
 Particle Theory of Light
 Photoelectric Effect – Photons of
light produce free electrons
LIGHT: Refraction of Light
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Refraction – Bending of light due to a
change in speed.
 Index of Refraction – Amount by which a
material refracts light.
 Prism – Glass that bends light. Different
frequencies are bent different amounts &
light is broken out into different colors.
Refraction
LIGHT & Reflection
 Reflection
– Bouncing back of light
waves
 Regular reflection – mirrors smooth
surfaces scatter light very little.
Images are clear & exact.
 Diffuse reflection – reflected light is
scattered due to an irregular surface.
Color of Light
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Color of Objects
 White light is the presence of ALL
the colors of the visible spectrum.
 Black objects absorb ALL the colors
and no light is reflected back.
How You See
Retina –
 Lens refracts light to converge on the
retina. Nerves transmit the image
 Rods –
 Nerve cells in the retina. Very
sensitive to light & dark
 Cones –
 Nerve cells help to see light/color
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How You See
Near Sighted –
Eyeball is too long
and image focuses in
front of the retina
 Far Sighted –
Eyeball is too short
so image is focused
behind the retina.
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© 2000 Microsoft Clip Gallery
© 2000 Microsoft Clip Gallery
LIGHT & USES: LASERS
 LASERS
 Acronym:
Light Amplification by
Stimulated Emission of Radiation
 Coherent Light – Waves are in phase
so it is VERY powerful & VERY
intense.
Summary
Waves carry energy from one place to
another
 The Electromagnetic Spectrum is an
arrangement of 7 kinds of radiation, based
on their wavelength
 Each kind of radiation has different
wavelengths
 Each color of light has different wavelengths
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Summary
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Radio waves, microwaves, infrared rays, light,
ultraviolet light, x-rays and gamma rays are
different wavelength bands in the spectrum of
electromagnetic waves
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The speed of EM radiation in vacuum is
approximately 186,000 miles/sec
The End…
© 2000 Microsoft Clip Gallery