physics Term - optic and wave

OPTICS AND WAVE
Acoustic shielding:	A sound barrier that prevents the transmission of acoustic energy.
Adiabatic:	Any change in which there is no gain or loss of heat.
Bar:	A unit of pressure, equal to 105 Pascals.
Acoustics:	The science of the production, transmission and effects of sound.
Afocal lens:	A lens of zero convergent power, whose focal points are infinitely distant.
Albedo:	The fraction of the total light incident on a reflecting surface, especially a celestial body, which is reflected back in all directions.
Amplitude:	The maximum absolute value attained by the disturbance of a wave or by any quantity that varies periodically.
Angle of contact:	The angle between tangents to the liquid surface and the solid surface inside the liquid, both the tangents drawn at the point of contact.
Angle of incidence:	The angle between the incident ray and the normal.
Angle of reflection:	The angle between the reflected ray and the normal.
Angle of refraction:	The angle between the refracted ray and the normal.
Angle of repose:	The angle of inclination of a plane with the horizontal such that a body placed on the plane is at the verge of sliding.
Angstrom:	A unit of length, 1 = 10-10 m.
Beat:	A phenomenon of the periodic variation in the intensity of sound due to superposition of waves differing slightly in frequency.
Brewster's law:	States that the refractive index of a material is equal to the tangent of the polarizing angle for the material.
Candela:	The S.I. unit of luminous intensity defined as the luminous intensity in a given direction of a source that emits monochromatic photons of frequency 540 x 1012 Hz & has a radiant intensity in that direction of 1/683 W/sr
Chromatic aberration:	An optical lens defect causing color fringes, because the lens brings different colors of light to focus at different points.
Critical angle:	The angle of incidence in a denser medium for which angle of refraction is .
Cyclotron:	A device used to accelerate the charged particles.
Decibel:	Unit of sound level, if P1 & P2 are two amounts of power, the first is said to be n decibels greater, where n = 10 log10 (P1/P2)
Diffraction:	The bending of light around the corners of an object.
Dioptre:	Unit of power of a lens.
Dispersion:	The splitting of white light into its component colors.
Doppler Effect:	The apparent change in the frequency of a wave due to relative motion between the source and the observer.
Fermat's principle:	An electromagnetic wave takes a path that involves the least time when propagating between two points.
Focus:	The point to which rays that are initially parallel to the axis of a lens or mirror are converged or from which they appear to diverge.
Fraunhoffer lines:	The dark lines in the spectrum of sun.
Frequency:	The number of oscillations completed in 1 second by an oscillating body.
Fundamental frequency:	The lowest frequency at which a system vibrates freely.
Hertz:	The unit of frequency, also known as cycles per second.
Huygens'principle:	Each point on a light wavefront can be regarded as a source of secondary waves, the envelope of these secondary waves determining the position of the wavefront at a later time.
Infrasonic:	Sound waves of frequency less than 20 Hz, below the range of human hearing.
Interference:	The redistribution of energy due to superposition of waves from coherent sources, resulting in alternate light and dark bands.
Light-year:	The distance traveled by light through empty space in one year, it is equal to 9.46 x 1012 km.
Longitudinal strain:	The ratio of change in length of a body to its initial length.
Longitudinal wave:	The particles of the medium oscillate in the direction of propagation of the wave.
Lyman series:	A group of lines in the ultraviolet region in the spectrum of hydrogen.
Magnetic wave:	The spread of magnetization from a small portion of a substance where an abrupt change in the magnetic field has taken place.
Magnification:	The ratio of the size of the image to the size of the object.
Malus law:	The intensity of the light transmitted from the analyzer varies directly as the square of the cosine of the angle between the plane of transmission of analyzer and polarizer.
Mechanical wave:	The waves, which need a material medium for their propagation, e.g., Sound waves.
Megahertz:	Unit of frequency, equal to 106 hertz.
Monochromatic light:	Consisting of single wavelength.
Natural frequency:	The frequency, with which a system oscillates in the absence of external forces, it depends on the size, composition, and shape of the object.
Optical fiber:	A long, thin thread of fused silica, used to transmit light, based on total internal reflection.
Oscillatory motion:	The to and fro motion of a body about its mean position.
Polaroid or polarizer:	A device that produces polarized light.
Period of oscillation:	The time required for one complete oscillation.
Periodic motion:	The motion which repeats itself after regular intervals of time.
Progressive wave:	A wave which transfers energy from one part of a medium to another.
Radiation:	The emission and propagation of waves transmitting energy through space or through some medium.
Rarefaction:	A part of a longitudinal wave in which the density of the particles of the medium is less than the normal density.
Real image:	An image which can be projected on a screen.
Reflection:	The bouncing back of a wave from a boundary.
Refraction:	The bending of light from its straight line path when it travels from one medium to another.
Refractive index:	The ratio of speed of light in vacuum to that in the medium.
Resolving power:	A quantitative measure of the ability of an optical instrument to produce separable images of different points of an object.
Resonance:	When the frequency of an external force matches the natural frequency of the body then the body oscillates with large amplitude.
Reverberation:	The prolongation of sound at a given point after direct reception from the source has ceased, it is due to reflections from the boundary surfaces.
Snell's law:	The ratio of sin i to sin r is a constant and is equal to the refractive index of the second medium with respect to the first.
Sonic boom:	Sound waves that pile up into a shock wave when a source is traveling at or faster than the speed of sound.
Standing waves:	The waves formed due to superposition of two waves of same frequency and traveling in opposite directions with same speed.
Total internal reflection:	Condition where all light is reflected back from a boundary between materials; occurs when light travels from denser to rarer medium and angle of incidence is greater than the critical angle.
Transverse wave:	A wave in which the particles of the medium oscillate in a direction perpendicular of the direction of propagation of wave.
Trough:	The point of maximum negative displacement on a transverse wave.
Ultrasonic Sound:	Sound waves of frequencies above 20,000Hz.
Unpolarized light:	Light consisting of transverse waves vibrating in all possible random directions.
Vibration:	A back and forth motion that repeats itself.
Virtual image:	An image formed when the reflected or refracted light rays appear to meet; this image cannot be projected on a screen.
Wave motion:	The movement of a disturbance from one part of a medium to another involving the transfer of energy but not the transfer of matter.
Wave period:	The time required for two successive crests or other successive parts of the wave to pass a given point.
Wave velocity:	The distance traveled by a wave in one second.
Wavelength:	The distance between the two nearest points on a wave, which are in the same phase or the distance between two adjacent crests or two adjacent troughs.