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Energy
The ability to do work.
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3 basic ways in which energy can be transferred
- 1. Conduction
- 2. Convection
- 3. Radiation
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Conduction
Occurs when a molecule or atom transfers its kinetic energy to another by colliding with it.
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Convection
Kinetic energy of atoms or molecules is transferred from one place to another by physically moving the atoms or molecules.
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Electromagnetic radiation
The only form of energy transfer that can take place in the vacuum of space.
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The 2 models of electromagnetic radiation
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Lambda
The shorthand for wavelength.
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Wavelength
The mean distance between consecutive maximums or minimums of a roughly periodic pattern; usually measured in micrometers or nanometers.
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Frequency
Number of wavelengths that pass a point per unit of time.
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Blackbody
A theoretical construct meaning a body that absorbs and radiates energy at the maximum possible rate per unit area at each wavelength for a given temperature.
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Relationship between temperature and energy emitted
The greater an object's temperature, the more radiant energy is emitted by it.
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Dominant wavelength of the Sun as it approximates a 6000 K blackbody
0.483 micrometers
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Dominant wavelength of the Earth as it approximates a 300 K blackbody
9.66 micrometers
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Visible light
Energy in the blue (0.4--0.5 micrometers), green (0.5--0.6 micrometers), and red (0.6--0.7 micrometers) bands of the electromagnetic spectrum.
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How are photons emitted?
Every time an electron jumps from a higher to a lower energy level, a photon moves away at the speed of light.
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What is the relationship between the frequency of radiation expressed by wave theory and the quantum?
The quantum's energy (in joules) = the Planck constant (6.626 * 10 -34 J s) * frequency of the radiation.
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What is the photoelectric effect?
Matter is heated so much that electrons break free from atoms, which are then referred to as ions. The radiation given off is unquantized, and a continuous spectrum is produced, rather than a band or series of bands. The surface of the Sun is an example.
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What is radiant energy?
The capacity of radiation within a spectral band to do work.
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What is the index of refraction?
The ratio of the speed of light in a vacuum, c, to the speed of light in a substance the light enters, cn.
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What are the 3 types of scattering?
- 1. Rayleigh
- 2. Mie
- 3. nonselective
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What are atmospheric windows?
Portions of the spectrum that transmit radiant energy effectively.
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What is radiant flux?
The time rate of flow of energy onto, off of, or through a surface; measured in watts.
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What is irradiance?
The amount of radiant flux incident upon a surface per unit area of that surface; measured in Watts per meter squared.
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What is exitance?
The amount of radiant flux leaving a surface per unit area of that surface; measured in Watts per meter squared.
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What is radiance?
The radiant intensity per unit of projected source area in a specified direction; measured in Watts per meter squared per steradian.
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