Electromagnetic radiation.
Electromagnetic radiation is made up of electric and magnetic fields of force continually interacting and propagating in the form of waves at the speed of light. Electromagnetic waves possess a continuous range of wavelengths from short-wavelength gamma rays through X rays, ultraviolet, visible, infrared and microwaves to long-wavelength radio waves. Light displays all the properties of wave phenomena. White (composite) light is composed of a range of wavelengths. The apparent brightness of light source varies inversely as the square of its distance.
Information in the spectrum of light.
The wavelengths, or spectral composition, of composite waves contain information about the physical nature of the light source and its environment. The study of the spectra, produced by dispersing white light into its constituent wavelengths, is called spectroscopy. Kirchhoff's laws are diagnostic in that one can infer the physical conditions of the light source by the type of spectrum its light forms: continuous, emission, absorption. Spectral lines in emission and absorption spectra uniquely identify the chemical composition of the emitting or absorbing gas. Three radiation lawsPlanck's, Stefan-Boltzmann, and Wien's-can be applied to the analysis of the continuous spectrum of a blackbody to determine its temperature. Thermal sources of radiation like the sun and stars emit radiant energy much like a blackbody. gained much information about the universe from the radiation it emits. And as we develop an even greater understanding of the nature of radiation-its formation, propagation, interaction with matter, and destruction-we can explore more deeply the dim sources in the outer reaches of the cosmos, almost back to the beginning of time.
Photons.
Electromagnetic radiation has properties showing it to be discrete as well as wavelike. Photons are discrete units of electromagnetic energy that have no inertia (are massless), are electrically neutral, and move at the speed of light. The energy content of a photon is inversely proportional to its wavelength. Photons are created by taking energy from atoms and destroyed by transferring their energy to the internal energy of atoms.
Emission and absorption of radiation.
The atomic processes responsible for the emission and absorption of photons are summarized in a model for the atom known as the Bohr atom. In hydrogen (and similarly for other atoms), the electron can occupy only a selected number of allowed orbits; that is, not all possible radius values are permitted for electron orbits; the electron normally resides in the lowest energy orbit, which is the one closest to the nucleus. Electrons make transitions to larger allowed orbits when atoms absorb photons and transitions to smaller allowed orbits when atoms emit photons. An electron can remain in a higher energy orbit for a very short time before it spontaneously drops to a lower energy state emitting a photon. All electron transitions beginning for absorption or ending for emission in an allowed energy state constitute a spectral series, such as the Balmer series in hydrogen. diffraction dispersion
Electromagnetic radiation is made up of electric and magnetic fields of force continually interacting and propagating in the form of waves at the speed of light. Electromagnetic waves possess a continuous range of wavelengths from short-wavelength gamma rays through X rays, ultraviolet, visible, infrared and microwaves to long-wavelength radio waves. Light displays all the properties of wave phenomena. White (composite) light is composed of a range of wavelengths. The apparent brightness of light source varies inversely as the square of its distance.
Information in the spectrum of light.
The wavelengths, or spectral composition, of composite waves contain information about the physical nature of the light source and its environment. The study of the spectra, produced by dispersing white light into its constituent wavelengths, is called spectroscopy. Kirchhoff's laws are diagnostic in that one can infer the physical conditions of the light source by the type of spectrum its light forms: continuous, emission, absorption. Spectral lines in emission and absorption spectra uniquely identify the chemical composition of the emitting or absorbing gas. Three radiation lawsPlanck's, Stefan-Boltzmann, and Wien's-can be applied to the analysis of the continuous spectrum of a blackbody to determine its temperature. Thermal sources of radiation like the sun and stars emit radiant energy much like a blackbody. gained much information about the universe from the radiation it emits. And as we develop an even greater understanding of the nature of radiation-its formation, propagation, interaction with matter, and destruction-we can explore more deeply the dim sources in the outer reaches of the cosmos, almost back to the beginning of time.
Photons.
Electromagnetic radiation has properties showing it to be discrete as well as wavelike. Photons are discrete units of electromagnetic energy that have no inertia (are massless), are electrically neutral, and move at the speed of light. The energy content of a photon is inversely proportional to its wavelength. Photons are created by taking energy from atoms and destroyed by transferring their energy to the internal energy of atoms.
Emission and absorption of radiation.
The atomic processes responsible for the emission and absorption of photons are summarized in a model for the atom known as the Bohr atom. In hydrogen (and similarly for other atoms), the electron can occupy only a selected number of allowed orbits; that is, not all possible radius values are permitted for electron orbits; the electron normally resides in the lowest energy orbit, which is the one closest to the nucleus. Electrons make transitions to larger allowed orbits when atoms absorb photons and transitions to smaller allowed orbits when atoms emit photons. An electron can remain in a higher energy orbit for a very short time before it spontaneously drops to a lower energy state emitting a photon. All electron transitions beginning for absorption or ending for emission in an allowed energy state constitute a spectral series, such as the Balmer series in hydrogen. diffraction dispersion
