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In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. [1] The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point.
For example, at 60 Hz, a 2000 MCM (1000 square millimeter) copper conductor has 23% more resistance than it does at DC. The same size conductor in aluminum has only 10% more resistance with 60 Hz AC than it does with DC. [14] Skin depth also varies as the inverse square root of the permeability of the conductor. In the case of iron, its ...
The differential equation above takes the form of 1D heat equation. The one-dimensional PDF below is the Green's function of heat equation (also known as Heat kernel in mathematics): P ( x , t ) = 1 4 π D t exp ( − ( x − x 0 ) 2 4 D t ) . {\displaystyle P(x,t)={\frac {1}{\sqrt {4\pi Dt}}}\exp \left(-{\frac {(x-x_{0})^{2}}{4Dt}}\right).}
SD g/mm 2 is the sectional density in grams per square millimeters; m g is the mass of the projectile in grams; d mm is the diameter of the projectile in millimeters; For example, a small arms bullet with a mass of 10.4 grams (160 gr) and having a diameter of 6.70 mm (0.264 in) has a sectional density of: 4 · 10.4 / (π·6.7 2) = 0.295 g/mm 2
In physics, the electric displacement field (denoted by D), also called electric flux density or electric induction, is a vector field that appears in Maxwell's equations. It accounts for the electromagnetic effects of polarization and that of an electric field, combining the two in an auxiliary field.
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.
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The operator is called the d'Alembertian (some authors denote this by only the square ). These equations are inhomogeneous versions of the wave equation, with the terms on the right side of the equation serving as the source functions for the wave. As with any wave equation, these equations lead to two types of solution: advanced potentials ...