The light particle conceived by Einstein is called a photon. The main point of his light quantum theory is the idea that light’s energy is related to its oscillation frequency (known as frequency in the case of radio waves). Photons have energy equal to their oscillation frequency times Planck’s constant.

Important applications of quantum theory include quantum chemistry, quantum optics, quantum computing, superconducting magnets, light-emitting diodes, the optical amplifier and the laser, the transistor and semiconductors such as the microprocessor, medical and research imaging such as magnetic resonance imaging and …

All matter exhibits wave-like behavior. For example, a beam of electrons can be diffracted just like a beam of light or a water wave. The concept that matter behaves like a wave was proposed by French physicist Louis de Broglie (/dəˈbrɔɪ/) in 1924. It is also referred to as the de Broglie hypothesis.

The group velocity of a wave is the velocity with which the overall envelope shape of the wave’s amplitudes—known as the modulation or envelope of the wave—propagates through space.

Particle velocity is the velocity of a particle (real or imagined) in a medium as it transmits a wave. The SI unit of particle velocity is the metre per second (m/s). In many cases this is a longitudinal wave of pressure as with sound, but it can also be a transverse wave as with the vibration of a taut string.

The phase velocity vp can be less than the speed of light. It can also be greater than the speed of light, but this does not violate special relativity because the single monochromatic wave or constant oscillation does not carry energy or information.

In the physical sciences, the wavenumber (also wave number or repetency) is the spatial frequency of a wave, measured in cycles per unit distance or radians per unit distance. Whereas temporal frequency can be thought of as the number of waves per unit time, wavenumber is the number of waves per unit distance.

In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave’s shape repeats. The inverse of the wavelength is called the spatial frequency.

Spatial frequency is a reciprocal length, which can thus be used as a measure of energy, usually of a particle. For example, the reciprocal centimetre, cm−1, is an energy unit equal to the energy of a photon with a wavelength of 1 cm. That energy amounts to approximately 1.24×10−4 eV or 1.986×10−23 J.

second

A time period (denoted by ‘T” ) is the time taken for one complete cycle of vibration to pass a given point. As the frequency of a wave increases, the time period of the wave decreases. The period of a pendulum is the time it takes from one side to the other and back.

The hertz (symbol: Hz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second.

Terahertz (unit), a unit of frequency, defined as one trillion (1012) cycles per second or 1012 hertz.

The hertz (symbol: Hz, definition: 1/s) is a unit derived from time which measures frequency in the International System of Units (SI). Frequency is how often something happens. A frequency of 1 hertz means that something happens once a second. The basic unit is 1/second.

The SI unit of frequency is the hertz (Hz). It is the property of sound that most determines pitch. The generally accepted standard hearing range for humans is 20 to 20,000 Hz. In air at atmospheric pressure, these represent sound waves with wavelengths of 17 metres (56 ft) to 1.7 centimetres (0.67 in).