The Characteristics of Electromagnetic Radiation

The Characteristics of Electromagnetic Radiation Oscillating amplitude of electric and magnetic field... 

Spectrometers are designed to measure the absorption of electromagnetic radiation by a sample. Basically, a spectrometer consists of a source of radiation, a compartment containing the sfflnple through which the radiation passes, and a detector. The frequency of radiation is continuously varied, and its intensity at the detector is compar ed with that at the source. When the frequency is reached at which the sample absorbs radiation, the detector senses a decrease in intensity. The relation between frequency and absorption is plotted as a spectrum, which consists of a series of peaks at characteristic frequencies. Its interpretation can furnish structural information. Each type of spectroscopy developed independently of the others, and so the data format is different for each one. An NMR spectrum looks different from an IR spectrum, and both look different from a UV-VIS spectrum. 

A further important property of synchrotron radiation concerns its polarization characteristics. The radiation is completely polarized, and the kind of polarization depends on the direction of the circulating electron beam as well as on the direction of photon emission. In order to understand these polarization properties, it is useful to recall the result for the emission of electromagnetic radiation from an electron moving with non-relativistic velocity in a circle the electric field vector follows the same shape and orientation as the projection of the electron s path onto a plane perpendicular to the observation direction. 

This characteristic blackbody spectrum holds for objects other than fireplace pokers. In fact, the spectrum of electromagnetic radiation emitted by any substance depends only on its temperature and is independent of the substance itself. 

Spectroscopy is the measurement of electromagnetic radiation absorbed, scattered, or emitted by chemical species. Because different chemical species and electromagnetic radiation interact in characteristic ways, it is possible to tailor instrumentation to detect these interactions specifically and quantitatively. A simple absorption spectrophotometer, depicted schematically in Figure 12.2, contains components that are common to many spectroscopic devices and are representative of many of the basic principles of instrumentation found in analytical biochemistry. 

By analogy with the characteristics of electron radiation, many anthors imagined that X-rays also corresponded to the propagation of particles. This debate over the particle or wave-like nature of electromagnetic radiation only comes to a close with... 

Thus, if a transition exists which is related to the frequency of the incident radiation by Planck s constant (h = 6.626-1 O 34), then the radiation can be absorbed. Conversely, if the frequency (v) does not satisfy Planck s expression, then the radiation will be transmitted. A plot of the frequency of the incident radiation against some measure of the percent radiation absorbed by the sample provides the absorption spectrum of the compound or component. The absorption spectrum is characteristic for the compound and this spectrum is often called the fingerprint of the compound. Infrared spectroscopy is based on the measurement of the absorption of electromagnetic radiation that arises from the altering of the vibration level of the component s molecule. An example of the adsorption and transmission of the infrared radiation is shown in Figure 2.30. 

Many of the properties of electromagnetic radiation are conveniently described by means of a classical sinusoidal wave model, which embodies such characteristics as wavelength, frequency, velocity, and amplitude, in contrast to other wave phenomena, such as sound, electromagnetic radiation requires no supporting medium for its transmission and thus passes readily through a vacuum. 

Just as with water waves, we can assign a frequency and wavelength to electromagnetic waves, as illustrated in FIGURE 6.3. These and all other wave characteristics of electromagnetic radiation are due to the periodic oscillations in the intensities of the electric and magnetic fields associated with the radiation. 

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