Download - A closer look at light…
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A closer look at light…
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• Light is a form of electromagnetic radiation that travels in waves.
• Most forms of EM radiation are invisible.• Light waves do not need a medium like water or
air to travel through. Empty space is fine.
WHAT IS LIGHT?
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Electromagnetic Radiation• Every object in the
universe emits some kind of radiation.
• The wavelength of light determines the characteristics of each form of radiation.
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1. If you listen to music on the radio = radio wave radiation.
2. If you use a microwave = microwave radiation
3. Military & police may use infrared goggles to see body heat in the dark = infrared radiation
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4. Visible light lets us see color.
5. An example of Ultra-violet radiation is a sunburn.
6. If you have an x-ray taken = x-ray radiation.
7. Radioactive materials emit Gamma ray radiation.
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Visible Light and the Prism• Visible white light is made
up of various colors as seen in a rainbow.
• When sunlight passes through a prism, the waves are refracted (bent) and a rainbow called a spectrum is produced.
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SPECTROSCOPE• A tool astronomers use to separate starlight
into a spectrum.• A prism is inserted into a telescope to split
the light into its colors.
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The spectroscope can tell astronomers...
• What a star is composed of• How hot a star is• How fast a star or galaxy is moving • The direction a star or galaxy is moving
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Types of Spectrums
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Continuous• An unbroken band of colors• The source emits light of all visible
wavelengths
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Emission • Unevenly spaced lines of different colors.• The source emits light of certain wavelengths. (l) • Every element has a unique emission spectrum.
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Absorption• A continuous spectrum crossed by dark lines.
• Determines elements in cool gases.
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Each element has a unique spectrum.
• By observing the spectra of distant stars we learned what elements make up the atmosphere of stars (and planets).
Argon
Helium
Mercury
Sodium
Neon
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The Doppler Effect
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Sound• Think about the sound a train makes as it approaches you
compared to when it moves away from you.
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• There is a change in the pitch of the sound.• High pitch sounds have a short wavelength• Low pitch sounds have a long wavelength.
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What is the Doppler Effect?
• The shift in the wavelength produced by a moving source.
• The change in pitch as something approaches you and moves away from you.
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LIGHT• Light with a long wavelength will appear red.• Light with a short wavelength will appear blue.
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• Approaching light = blue• Leaving light = red
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Red Shift• A star or galaxy
moving away from the Earth will produce a shift in its spectrum towards the red end.
Sun Galaxy
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Edwin Hubble observed most galaxies in the universe show a red shift.
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What does that mean about our Universe?
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It’s Expanding!!!
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The Big Bang Theory• Red shifts are evidence
supporting the Big Bang.• It’s the dominant scientific
theory about the origin of the universe
• The universe was created sometime ~ 10-20 billion years ago from a cosmic explosion that hurled matter in all directions.