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The Planck constant, or Planck's constant, denoted by , [1] is a fundamental physical constant [1] of foundational importance in quantum mechanics: a photon's energy is equal to its frequency multiplied by the Planck constant, and the wavelength of a matter wave equals the Planck constant divided by the associated particle momentum.
A standing wave, also known as a stationary wave, is a wave whose envelope remains in a constant position. This phenomenon arises as a result of interference between two waves traveling in opposite directions. The sum of two counter-propagating waves (of equal amplitude and frequency) creates a standing wave. Standing waves commonly arise when ...
equivalent to approximately 114 megawatts of constant power output. The watt-second is a unit of energy, equal to the joule. One kilowatt hour is 3,600,000 watt seconds. While a watt per hour is a unit of rate of change of power with time, [iii] it is not correct to refer to a watt (or watt-hour) as a watt per hour. [36]
The standard example of a longitudinal wave is a sound wave or "pressure wave" in gases, liquids, or solids, whose oscillations cause compression and expansion of the material through which the wave is propagating. Pressure waves are called "primary waves", or "P-waves" in geophysics. Water waves involve both longitudinal and transverse motions ...
A sound wave is a variation in air pressure, while in light and other electromagnetic radiation the strength of the electric and the magnetic field vary. Water waves are variations in the height of a body of water. In a crystal lattice vibration, atomic positions vary. The range of wavelengths or frequencies for wave phenomena is called a spectrum.
For example, the pressure of electromagnetic radiation on an object derives from the transfer of photon momentum per unit time and unit area to that object, since pressure is force per unit area and force is the change in momentum per unit time. [33]
The maximum work is thus regarded as the diminution of the free, or available, energy of the system (Gibbs free energy G at T = constant, P = constant or Helmholtz free energy F at T = constant, V = constant), whilst the heat given out is usually a measure of the diminution of the total energy of the system (internal energy).
α, the fine-structure constant, (≈ 1 / 137 ). This is also the square of the electron charge, expressed in Planck units, which defines the scale of charge of elementary particles with charge. The electron charge is the coupling constant for the electromagnetic interaction.