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In physics and many other areas of science and engineering the intensity or flux of radiant energy is the power transferred per unit area, where the area is measured on the plane perpendicular to the direction of propagation of the energy. [a] In the SI system, it has units watts per square metre (W/m 2), or kg⋅s −3 in base units.
Different fields of application have different definitions for the term. All the meanings are very similar in concept: In chemistry, the transmission coefficient refers to a chemical reaction overcoming a potential barrier; in optics and telecommunications it is the amplitude of a wave transmitted through a medium or conductor to that of the incident wave; in quantum mechanics it is used to ...
The ratio of waves' electric field (or magnetic field) amplitudes are obtained, but in practice one is more often interested in formulae which determine power coefficients, since power (or irradiance) is what can be directly measured at optical frequencies. The power of a wave is generally proportional to the square of the electric (or magnetic ...
The electric field strength at a specific point can be determined from the power delivered to the transmitting antenna, its geometry and radiation resistance. Consider the case of a center-fed half-wave dipole antenna in free space, where the total length L is equal to one half wavelength (λ/2). If constructed from thin conductors, the current ...
is the surface which multiplied by the power per unit surface of the incoming wave, gives the maximum available power. The maximum power that an antenna can extract from the electromagnetic field depends only on the gain of the antenna and the squared wavelength . It does not depend on the antenna dimensions.
For example, the average power transmitted by an acoustic or electromagnetic wave or by an electrical signal is proportional to the square of the RMS amplitude (and not, in general, to the square of the peak amplitude). [6] For alternating current electric power, the universal
In radio transmission, transmitter power output (TPO) is the actual amount of power (in watts) of radio frequency (RF) energy that a transmitter produces at its output. [ 1 ] TPO is a concept related to effective radiated power (ERP), but refers to the power output of a transmitter, without accounting for antenna gain.
Sound intensity, also known as acoustic intensity, is defined as the power carried by sound waves per unit area in a direction perpendicular to that area, also called the sound power density and the sound energy flux density. [2] The SI unit of intensity, which includes sound intensity, is the watt per square meter (W/m 2).