emissivity

Examples of emissivity in the following topics:

• Lasers

  • It does so through a process of optical amplification based on the stimulated emission of photons.
  • This is the mechanism of fluorescence and thermal emission.
  • This "induced" decay process is called stimulated emission.
  • In stimulated emission, the decaying atom produces an identical "copy" of the incoming photon.
  • Identify process that generates laser emission and the defining characteristics of laser light

• Emission

  • Generally material has two routes for the emission of radiation: stimulated emission and spontaneous emission.
  • The spontaneous emission is independent of the radiation field.
  • Let's define the spontaneous emission coefficient, $j$.
  • Often the emission is isotropic and it is convenient to define the emissivity of the material per unit mass

• Calculating carbon footprints

  • Calculating a ‘carbon footprint' (i.e. the amount of carbon dioxide a process creates) is a trendy way to measure carbon emissions with the added benefit that, when lowered, the numbers can be used in public relations campaigns or to prove compliance with emissions legislation.
  • Employees usually enjoy seeing how their efforts help reduce environmental degradation so displaying carbon emission reductions alongside other relevant data can help create motivation and a strong sense of achievement.

• Emission Spectrum of the Hydrogen Atom

  • The emission spectrum of atomic hydrogen is divided into a number of spectral series.
  • The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted by an atom's electrons when they are returned to a lower energy state.
  • Each element's emission spectrum is unique, and therefore spectroscopy can be used to identify elements present in matter of unknown composition.
  • Similarly, the emission spectra of molecules can be used in chemical analysis of substances.
  • Explain how the lines in the emission spectrum of hydrogen are related to electron energy levels.

• Quotas

  • It then allocates emissions permits up to the specified limit among firms.
  • Firms are required to hold a number of permits equivalent to their emissions.
  • Firms that need to increase their volume of emissions must buy permits from firms that require fewer of them.
  • Firms that have a high cost of reducing emissions are willing to pay for the permits, while those that can reduce emissions in the most cost-efficient manner will do so and sell their permits.
  • In the United States there is a national market for sulfur dioxide emissions to reduce acid rain.

• General energy reduction

  • Some electricity providers invest in wind, solar or tidal energy and provide these options to their customers so they can cut CO2 emissions.
  • This not only saves money, the resulting drop in electricity reduces greenhouse gas emissions.
  • If all Europeans changed their standard light bulbs to energy efficient bulbs the resulting drop in carbon emissions would be equivalent to taking 70% of the continent's cars off the road.
  • If everybody in the USA paid his or her bills online, the nation's annual paper waste would be reduced by 1.6 tons and greenhouse gas emissions would be cut by 2.1 million tons.

• Aurora Borealis and the Aurora Australis

  • Collisions with other atoms or molecules can absorb the excitation energy and prevent emission.
  • Oxygen emissions are green or brownish-red, depending on the amount of energy absorbed.
  • Nitrogen emissions are blue if the atom regains an electron after it has been ionized and red if the atom returns to ground state from an excited state.
  • Collisions become more frequent farther down in the atmosphere, and red emissions do not have time to happen; eventually, even green light emissions are prevented.
  • This is why there is a color differential with altitude: at high altitudes, oxygen's red emissions remain; then, oxygen's green emissions and nitrogen's blue and red emissions; and finally, only nitrogen's blue and red emissions are left, because collisions prevent oxygen from emitting any light at all.

• Calculating the Emission and Absorption Coefficients

  • We can write the emission and absorption coefficients in terms of the Einstein coefficients that we have just examined.
  • The emission coefficient $j_\nu$ has units of energy per unit time per unit volume per unit frequency per unit solid angle!
  • The Einstein coefficient $A_{21}$ gives spontaneous emission rate per atom, so dimensional analysis quickly gives

• Another twist: capitalizing on guilt

  • The company made its purchase under the belief that laws would soon be enacted that limited carbon emissions and that these same laws would probably give companies struggling to reduce their carbon emissions the option of offsetting them.
  • (Ellison, Katherine, ‘Shopping for Carbon Credits') A growing number of businesses have since climbed onto the bandwagon by allowing customers to offset their carbon emissions by purchasing carbon credits.
  • For example, some airlines will voluntarily add a few dollars to the price of their tickets and several power companies provide the option of paying a higher monthly fuel bill to help offset carbon emissions.
  • In other examples, Range Rover automobiles offered an emissions offset for the first 45,000 miles (72,000 kilometres) which was factored into their purchase price and a ski resort in Vail, Colorado, once enticed skiers to buy energy credits to help buy a wind turbine so in the future the skiers will be carbon-neutral when they are lifted to the top of a nearby mountain.

• Problems

  • What is the synchrotron emission from a single electron passing through a magnetic field in terms of the energy density of the magnetic field and the Lorentz factor of the electron?
  • What is the inverse Compton emission from a single electron passing through a gas of photons field in terms of the energy density of the photons and the Lorentz factor of the electron?
  • What is the total inverse Compton emission from the region if you assume that the synchrotron emission provides the seed photons for the inverse Compton emission?