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Electromagnetic Spectrum Absorption

April 15, 2013

Introduction

The range of all possible frequencies of electromagnetic radiation is termed as electromagnetic spectrum. The “electromagnetic spectrum” of an object is the distinguishing distribution of electromagnetic radiation emitted or absorbed by that particular object.

The electromagnetic spectrum extends from low frequencies which are used for modern radio to gamma radiation at the short-wavelength end, covering wavelengths from thousands of kilometers to a fraction of the size of an atom. The long wavelength limits to the size of the universe itself, while it is thought that the short wavelength limits in the vicinity of the Planck length, although in principle the spectrum is infinite and continuous.

Absorption spectroscopy

Absorption spectroscopy refers to spectroscopic techniques which measure the absorption of radiation, as a function of frequency or wavelength, because of its interaction with a sample. The sample absorbs energy in the form of photons from the radiating field. The intensity of the absorption differs as a function of frequency, and this variation is termed as the absorption spectrum. Absorption spectroscopy is performed transversely to the electromagnetic spectrum.

There is a wide range of experimental approaches to measure absorption spectra. The most common arrangement is to direct a generated beam of radiation at a sample and to detect the intensity of the radiation which passes through it. The transmitted energy can be used for calculating the absorption. The source, sample arrangement and detection technique differ significantly depending on the frequency range and the purpose of the experiment.

Applications of Electromagnetic spectrum

Absorption spectroscopy is useful in chemical analysis due to its specificity and its quantitative nature. The specificity of absorption spectra allows compounds to be varied from one another in a mixture. Absorption spectroscopy is used for identification of pollutants in air, differentiating the pollutant from the nitrogen, oxygen, water and the other expected constituents.

An absorption spectrum can quantitatively relate to the amount of material present using the Beer-Lambert law. Determination of the absolute concentration of a compound needs knowledge of the compound’s absorption coefficient. The absorption coefficient can be determined by measuring the spectrum of a calibration standard with a known concentration of the target.

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