Download - How is Light Produced?
![Page 1: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/1.jpg)
How is Light Produced?
• It’s all tied to energy
• Energy of the material’s temperature
• Energy levels within atoms
![Page 2: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/2.jpg)
Motivation
• If we understand how light is produced, then when we see light we’ll know the conditions under which it was created.
• Examples: – That scope thing Spock uses– Atmospheric composition of a newly
discovered planet– Can a given star support life?
![Page 3: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/3.jpg)
Kirchoff’s Laws - 3 types of spectra
• Continuous or Continuum – Ex: Blackbody radiation
• Emission• Absorption
![Page 4: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/4.jpg)
Hot solid thing
Hot gaseous
thing
Transparent thing blocking other hot thing
![Page 5: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/5.jpg)
Hot dense thing
![Page 6: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/6.jpg)
Continuous Spectrum
• Continuous, continuum
• All colors
• Examples: stars are nearly blackbody, incandescent light bulbs, electric burners, people, etc.
![Page 7: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/7.jpg)
Causes of Continuum• Blackbody
– Thermal– Hot dense material
• Bremsstrahlung / Free-free– An electron passes by a proton / nucleus
• Recombination / Free-bound– Electron captured by a proton / nucleus
• Compton Scattering – Existing photon has its wavelength
changed by a collision
![Page 8: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/8.jpg)
http://www.oswego.edu/~kanbur/a100/images/planck.jpg
(Assuming stars are
same size.)
![Page 9: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/9.jpg)
Planck’s Law
• Completely describes the light (blackbody radiation) coming from an object.
![Page 10: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/10.jpg)
Stefan-Boltzmann Law
• L=σT4×star’s surface area
• The total brightness of an object (at all colors added together) depends on the Temperature to the 4th power (and size of the object).
• Temperature makes objects glow. The hotter it is, the more it glows.
![Page 11: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/11.jpg)
http://www.oswego.edu/~kanbur/a100/images/planck.jpg
(Assuming stars are
same size.)
![Page 12: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/12.jpg)
Wein’s Law
• λmax=2,900,000/T (in nm)• What color an object is brightest at
depends on the Temperature of the object.
• Hotter objects are brightest in blue/purple (and ultraviolet).
• Cooler objects are brightest in red (and infrared).
![Page 13: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/13.jpg)
http://hypertextbook.com/physics/modern/planck/
Hottest stars look blue
Our Sun looks yellow
Cool stars look red
(Assuming same size
stars.)
![Page 14: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/14.jpg)
How can you tell which object is hotter/larger
1. Color of the peak tells us the object’s temperature.
2. If two objects have the same color, the brighter one is physically larger.
3. If two objects of the same size, the hotter one will be brighter at all colors.
![Page 15: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/15.jpg)
Hot gaseous
thing
![Page 16: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/16.jpg)
Emission Spectrum
• Hot thin gas
• Only a few select colors
• Examples: some fluorescent lights, neon lights, natural gas flames, warm gas clouds in space
![Page 17: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/17.jpg)
http://astronomy.nmsu.edu/nicole/teaching/ASTR110/lectures/lecture19/pics/emission_spectra.gif
![Page 18: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/18.jpg)
![Page 19: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/19.jpg)
http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png
When an electron goes down an orbital
![Page 20: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/20.jpg)
http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png
A photon comes out of a specific color
![Page 21: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/21.jpg)
Absorption Spectrum
• Hot dense object blocked by cool thin gas
• Continuum minus emission• All colors except a select few• Examples: nearby gas cloud blocks a
farther star, nearer galaxy blocks a far quasar, sunglasses block sunlight, Earth’s atmosphere blocks sunlight
![Page 22: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/22.jpg)
Transparent thing blocking other hot thing
![Page 23: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/23.jpg)
http://www.solarobserving.com/pics/hydrogen-spectra.jpg
![Page 24: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/24.jpg)
Absorption and emission spectra are opposite in appearance and cause.
![Page 25: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/25.jpg)
Emission spectrum
Electrons go down levels on their own and put out light as a result.
![Page 26: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/26.jpg)
http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png
When an electron goes down an orbital
![Page 27: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/27.jpg)
http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png
A photon comes out of a specific color
![Page 28: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/28.jpg)
Absorption Spectrum
Light of all colors comes in. When the color is just right, it makes the electron pop up to a higher level.
![Page 29: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/29.jpg)
http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png
Light of all colors comes in
![Page 30: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/30.jpg)
http://upload.wikimedia.org/wikipedia/commons/thumb/5/55/Bohr-atom-PAR.svg/310px-Bohr-atom-PAR.svg.png
Only the right color of light is used up to make the electron jump up orbitals
![Page 31: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/31.jpg)
http://www.physics.umd.edu/courses/Phys401/bedaque06/discrete_spectra.jpg
bright emission lines become dark absorption lines
![Page 32: How is Light Produced?](https://reader036.vdocuments.us/reader036/viewer/2022070411/568148f0550346895db60d49/html5/thumbnails/32.jpg)
Conclusion
• Colors of light (how many colors and how bright) call tell us the temperature, density, composition, and even shape of an object.