How do atoms and molecules interact with light waves and sound waves?

When a light wave encounters an object, it is transmitted, reflected, absorbed, refracted, polarized, diffracted or scattered depending on the. Atoms are too small to be seen directly, even with the most powerful optical microscopes. However, atoms interact with light and, in some circumstances, emit it in ways that reveal their internal structures in amazing detail. It is through the language of light that we communicate with the world of the atom.

This section will introduce you to the rudiments of this language. As the temperature increases, the wavelengths decrease; at room temperature, most of the emission occurs in the infrared. Maxwell was able to calculate the speed at which electromagnetic disturbances propagate and discovered that this speed is the same as that of light. The electromagnetic spectrum is conventionally divided into several parts, as shown in the following diagram, in which the four logarithmic scales correlate the wavelength of electromagnetic radiation with its frequency in hertz (units of s) and the energy per photon, expressed in both joules and electronvolts.

The electronic structure of an atom can only be determined indirectly by looking at the way in which atoms absorb and emit light. Electron diffraction has become an important tool for investigating the structures of molecules and solid surfaces. This scattering of light at shorter wavelengths illuminates the skies with light from the blue and violet end of the visible spectrum. While it can be said that waves are blocked by certain materials, the correct understanding is that the wavelengths of energy are either absorbed by objects or not.

Lasers aboard NASA's Lunar Reconnaissance Orbiter use this light-reflecting behavior to map the surface of the Moon. When light wave interference experiments are carried out with extremely low light intensities, wave theory breaks down; instead of recording a smooth succession of interference patterns as shown above, an extremely sensitive detector sees individual pulses, that is, individual photons. But Einstein's 1905 explanation of the photoelectric effect showed that light also has a nature similar to that of particles. Two small flashlight batteries will produce about 2.5 volts and could therefore, in principle, provide an electron with approximately the same amount of kinetic energy that blue-green light can supply.

The atom has a 50% chance of decay in one hour, which means that its wave representation will contain both possibilities until an observation is made.

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