© 2005 pearson education inc., publishing as addison-wesley light: the messenger
Post on 19-Dec-2015
215 views
TRANSCRIPT
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Light: The Messenger
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
• Homework #3 Due Friday, covers Chapt. 5-8
• 6 Problems - Some Quantitative with equations
• Telescope on Campbell: Tue & Thu 7-8
• Midterm: Thursday, February 26 (14 days)
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
What is a Planet Made of ?What is a Planet Made of ?
• Chemical Composition of its surface and atmosphere ?
• Temperature = ?• Is it:
Ice ?
Liquid?
Gas?
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
The “Dwarf Planet”, Eris and its moon, Dysnomia. It is twice as far as Pluto and is larger than Pluto. Numerous other icy objects larger than Pluto likely exist in the Kuiper Belt of the far distant Solar System.
Discovered: April 2006 (Mike Brown).
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Artist’sArtist’sRenderingRendering
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Light in Everyday Life
and in the Universe
• Type of Energy that Moves through space
• Composed of different wavelengths (colors)
• Atoms and Molecules Emit Light
• Atoms and Molecules Absorb Light
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Light Power:Energy per Second
• Power: the rate at which energy is emitted or used.• Measured in units called watts.
1 watt = 1 joule per second
• A 100 watt light bulb emits 100 joules of energy* every second.
• 1 kilowatt-hour: 1000 Joules/sec during 1 hour * Light Energy
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Properties of Light
• Light can act as a wave: “Electromagnetic wave”
• Light can act as a particle: “photon”
• Light has wavelength and frequency.
• Light travels at the speed of … Light: 300,000 km/s300,000 km/s
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Light as a Wave
A wave is a pattern which is revealed by its interaction with particles.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Light as a WaveLight as a Wave
• f = frequency = wavelength• wave speed = f • Speed of light is “c”
= 300,000 km/s • For light: f = c• The higher f is, the
smaller is, and vice versa.
• Our eyes recognize f (or ) as ccoolloorr .
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Light as Photons• Light can also act as photons – particles of
light energy.• The energy carried by each photon depends
on its frequency (color) E = hf = hc / [“h” is called Planck’s Constant]
• Bluer light carries more energy per photon.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Demo:
Solar Cell -photons carry energy,
absorbed by solar panel:makes a motor turn
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Domains of Wavelengths of Light
• “Electromagnetic spectrum” :
Light waves of all wavelengths
Gamma Rays (shortest wavelength: 10-10 meter)
X-Rays
Ultraviolet
Visible (0.5 x 10-6 meters)
Infrared (1-10 x10-6 meters)
Radio Waves (0.001 meter or more)
© 2005 Pearson Education Inc., publishing as Addison-Wesley
The Electromagnetic SpectrumMost wavelengths of light can not be seen by the human eye.
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Summary
Light
A vibration in an electromagnetic field moving through space.Energy is carried by light.
Light as a wave
Light as a particle E = hf photon
f = c
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Atoms and Molecules Interact with Light
1. Emission – atoms and molecules release energy as light
2. Absorption – atoms and molecules absorb light energy
3. Reflection – Light bounces off matter.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Light and Matter:
• Atoms and Molecules emit light at specific wavelengths. Each atom and molecule emits a unique set of wavelengths.
• Solid Objects Emit “Thermal radiation”: Light at all wavelengths.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
EmissionSpectrafrom atoms and molecules
• Each type of atoms has a unique set of electron energy levels.
• Each atoms emits its own set of wavelengths:
• Like fingerprints.• A hot gas of one type of
atom emits photons having wavelengths
specific to that atom:• Emission line spectrum.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Demonstration: H and Ne
Emission TubesUse diffraction gratings
on tubes, computer screen, laser pointer
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Energy Levels of Atoms
• Electron is allowed to have certain energies in an atom.
• Electrons can absorb light and gain energy or emit light when they lose energy.
• Consider light as a photon when discussing its interaction with matter.
• Only photons whose energies (colors) equal the difference in electron energy levels can be emitted or absorbed.
HydrogenAtom
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Absorption of Lightby atoms or molecules
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Absorption of Light by Atoms & Molecules
• When light shines through a gas, atoms will absorb those photons whose wavelengths match the atom’s electron energy levels.
• The resulting spectrum has all wavelengths (all colors), but is missing those wavelengths that were absorbed.
• You can determine which atoms are in an object by the You can determine which atoms are in an object by the emission & absorption lines in the spectrum.emission & absorption lines in the spectrum.
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Warm, Solid Objects Glow by
Thermal Emission of Light
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Cool Warmer Hot HotterCool Warmer Hot HotterRed & Faint White & BrightRed & Faint White & Bright
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Warm, Solid Objects Emit Light:“Thermal Emission”
Examples:Examples:
Electric Stove Electric Stove FilamentsFilaments
Hot fireplace Hot fireplace CoalsCoals
Light bulbLight bulbfilamentfilament
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Light carries informationabout the Planets and Stars
By studying the spectrum of an object, we can learn its:1 Composition2 Temperature3 Velocity
Key: Separate light into its different wavelengths (spectrum).
© 2005 Pearson Education Inc., publishing as Addison-Wesley
Summary of Demos:• E+50+20 Prism - to be used with overhead projector• E + 15 + 25 Discharge tubes: view with diffraction gratings, Neon and
hydrogen. Can tell composition from pattern of lines.• include: 100 slide-mounted diffraction gratings & 50 stick-mounted
gratings, all in the physics stockroom under E + 15 + 25• Comes with E+50_20: Carbon or Tungsten lamp with variac:
change temp. and view with the diffraction gratings to see blue emerge. Blackbody radiation: hot --> blue
• F+15+20 Solar-cell-powered helicopter• Doppler: spin buzzer overhead.
More gratings are in 264 Evans (TALC room).