 Polarization also polarization is a property applying to transverse waves that specifies the geometrical orientation of the oscillations. In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. A simple example of a polarized transverse wave is vibrations traveling along a top string C image for example, in a musical instrument like a guitar string. Depending on how the string is plucked, the vibrations can be in a vertical direction, horizontal direction, or at any angle perpendicular to the string. In contrast, in longitudinal waves, such as sound waves in a liquid or gas, the displacement of the particles in the oscillation is always in the direction of propagation, so these waves do not exhibit polarization. Transverse waves that exhibit polarization include electromagnetic waves such as light and radio waves, gravitational waves, and transverse sound waves, shear waves in solids. In some types of transverse waves, the wave displacement is limited to a single direction, so these also do not exhibit polarization. For example, in surface waves in liquids gravity waves the wave displacement of the particles is always in a vertical plane. An electromagnetic wave such as light consists of a couple of oscillating electric field and magnetic field which are always perpendicular, by convention, the polarization of electromagnetic waves refers to the direction of the electric field. In linear polarization, the fields oscillate in a single direction. In circular or elliptical polarization, the fields rotate at a constant rate in a plane as the wave travels. The rotation can have two possible directions. If the fields rotate in a right-hand sense with respect to the direction of wave travel, it is called right-circular polarization, or, if the fields rotate in a left-hand sense, it is called left-circular polarization. Light or other electromagnetic radiation from many sources, such as the sun, flames, and incandescent lamps, consists of short-wave trains with an equal mixture of polarizations, this is called unpolarized light. Polarized light can be produced by passing unpolarized light through a polarizing filter, which allows waves of only one polarization to pass through. The most common optical materials such as glass are isotropic and do not affect the polarization of light passing through them, however, some materials those that exhibit birefringence, dichroism, or optical activity can change the polarization of light. Some of these are used to make polarizing filters. Polarizing is also partially polarized when it reflects from a surface.