SO stuffs

Waves - Examples of wave-like phenomena are light, water waves, and sound waves.

- Frequency is a measure of the number of occurrences of a repeating event per unit time.

- The period of a wave is the time the full wave takes to pass a given point

- Longitudinal waves are waves that have vibrations along or parallel to their direction of travel; that is, waves in which the motion of the medium is in the same direction as the motion of the wave.

- A standing wave, also known as a stationary wave, is a wave that remains in a constant position

- Refraction is the change in direction of a wave due to a change in its speed.This is most commonly seen when a wave passes from one medium to another. Refraction of light is the most commonly seen example, but any type of wave can refract when it interacts with a medium.

- Reflection is the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves.

- Diffraction refers to various phenomena associated with the bending of waves when they interact with obstacles in their path. It occurs with any type of wave, including sound waves, water waves, and electromagnetic waves such as visible light, x-rays and radio waves

- Primary light colors: Violet, blue, green, yellow, orange , red

- The electromagnetic spectrum is the range of all possible electromagnetic radiation. The "electromagnetic spectrum" (usually just spectrum) of an object is the characteristic distribution of electromagnetic radiation from that object.
The electromagnetic spectrum, extends from below the frequencies used for modern radio (at the long-wavelength end) through gamma radiation (at the short-wavelength end), covering wavelengths from thousands of kilometers down to a fraction the size of an atom. In our universe the short wavelength limit is likely to be in the vicinity of the Planck length, and the long wavelength limit is the size of the universe itself (see physical cosmology), though in principle the spectrum is infinite and continuous.

- The Doppler effect is the change in frequency and wavelength of a wave as perceived by an observer moving relative to the source of the waves. For waves that propagate in a wave medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source or motion of the observer or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as light or gravity in special relativity, only the relative difference in velocity between the observer and the source needs to be considered.

- In physics, wavelength is the distance between repeating units of a propagating wave of a given frequency. It is commonly designated by the Greek letter lambda (λ). Examples of wave-like phenomena are light, water waves, and sound waves.
Wavelength λ is inverse proportional with the frequency, the number of wave periods per time unit passing a given point, as in

where vw is the propagation velocity of the wave. In the case of electromagnetic radiation, such as light, in a vacuum, this speed is the speed of light, 299,792,458 m/s or about 3x108 m/s. For sound waves in air, this is the speed of sound, 344 m/s (1238 km/h) in air at room temperature. Usually, SI units are used, where the wavelength is expressed in meters, the frequency in Hz, and the propagation velocity in meters per second.

- A transverse wave is a traveling wave, a wave that propagates (travels) in a direction perpendicular to the direction in which the oscillations that produce the wave are moving. For example: if a transverse wave is moving in the positive x-direction, its up and down oscillations are in up and down directions that lie in the yz-plane.
Light is composed of transverse waves. See electromagnetic spectrum for information on different types of electromagnetic waves. Electromagnetic waves are transverse waves.

- Electromagnetic radiation is a self-propagating wave in space with electric and magnetic components.

- Wave propagation is any of the ways in which waves travel through a medium.

- A waveguide is a structure which guides waves, such as electromagnetic waves, light, or sound waves. There are different types of waveguide for each type of wave.

- An element's emission spectrum is the relative intensity of electromagnetic radiation of each frequency it emits when it is heated (or more generally when it is excited).

When the electrons in the element are excited, they jump to higher energy levels. As the electrons fall back down, and leave the excited state, energy is re-emitted, the wavelength of which refers to the discrete lines of the emission spectrum. Note however that the emission extends over a range of frequencies, an effect called spectral line broadening.
The emission spectrum can be used to determine the composition of a material, since it is different for each element of the periodic table. One example is identifying the composition of stars by analyzing the received light.

An absorption spectrum occurs when light passes through a cold, dilute gas and atoms in the gas absorb at characteristic frequencies; since the re-emitted light is unlikely to be emitted in the same direction as the absorbed photon, this gives rise to dark lines (absence of light) in the spectrum. The light emitted from an excited atom can not be directed toward the observer, so the light appears to be missing from the continuous spectrum.

- A material's absorption spectrum shows the fraction of incident electromagnetic radiation absorbed by the material over a range of frequencies. An absorption spectrum is, in a sense, the opposite of an emission spectrum.

Every chemical element has absorption lines at several particular wavelengths corresponding to the differences between the energy levels of its atomic orbitals. For example, an object that absorbs blue, green and yellow light will appear red when viewed under white light. Absorption spectra can therefore be used to identify elements present in a gas or liquid. This method is used in deducing the presence of elements in stars and other gaseous objects which cannot be measured directly.

- Interference is the addition (superposition) of two or more waves that results in a new wave pattern.
As most commonly used, the term interference usually refers to the interaction of waves which are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency.

- Consider two waves that are in phase,with amplitudes A1 and A2. Their troughs and peaks line up and the resultant wave will have amplitude A = A1 + A2. This is known as constructive interference.

- If the two waves are pi radians, or 180°, out of phase, then one wave's crests will coincide with another wave's troughs and so will tend to cancel out. The resultant amplitude is A = | A1 − A2 | . If A1 = A2, the resultant amplitude will be zero. This is known as destructive interference.

- Radio waves are electromagnetic waves occurring on the radio frequency portion of the electromagnetic spectrum. A common use is to transport information through the atmosphere or outer space without wires. Radio waves are distinguished from other kinds of electromagnetic waves by their wavelength, a relatively long wavelength in the electromagnetic spectrum.

- In most of the world, the FM broadcast band, used for broadcasting FM radio stations, goes from 87.5 to 108.0 MHz.

- In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency (contrast this with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant)

- Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. AM works by varying the strength of the transmitted signal in relation to the information being sent. For example, changes in the signal strength can be used to reflect the sounds to be reproduced by a speaker, or to specify the light intensity of television pixels.