Electric potential

An electric potential is the amount of work needed to move a unit of charge from a reference point to a specific point inside the field without producing an acceleration. The reference point is the Earth or a point at infinity, although any point can be used. In classical electrostatics, the electrostatic field is a vector quantity, expressed as the gradient of the electrostatic potential, a scalar quantity denoted by V or φ, equal to the electric potential energy of any charged particle at any location divided by the charge of that particle. By dividing out the charge on the particle a quotient is obtained, a property of the electric field itself. In short, electric potential is the electric potential energy per unit charge; this value can be calculated in either a static or a dynamic electric field at a specific time in units of joules per coulomb, or volts. The electric potential at infinity is assumed to be zero. In electrodynamics, when time-varying fields are present, the electric field cannot be expressed only in terms of a scalar potential.

Instead, the electric field can be expressed in terms of both the scalar electric potential and the magnetic vector potential. The electric potential and the magnetic vector potential together form a four vector, so that the two kinds of potential are mixed under Lorentz transformations. Electric potential is always a continuous function in space. An idealized point charge has 1 / r potential, continuous everywhere except the origin; the electric field across an idealized surface charge is not continuous, but it's not infinite at any point. Therefore, the electric potential is continuous across an idealized surface charge. An idealized linear charge has ln ⁡ potential, continuous everywhere except on the linear charge. Classical mechanics explores concepts such as force, potential, etc. Force and potential energy are directly related. A net force acting on any object will cause it to accelerate; as an object moves in the direction in which the force accelerates it, its potential energy decreases.

For example, the gravitational potential energy of a cannonball at the top of a hill is greater than at the base of the hill. As it rolls downhill its potential energy decreases, being translated to kinetic energy, it is possible to define the potential of certain force fields so that the potential energy of an object in that field depends only on the position of the object with respect to the field. Two such force fields are an electric field; such fields must affect objects due to the intrinsic properties of the object and the position of the object. Objects may possess a property known as electric charge and an electric field exerts a force on charged objects. If the charged object has a positive charge the force will be in the direction of the electric field vector at that point while if the charge is negative the force will be in the opposite direction; the magnitude of the force is given by the quantity of the charge multiplied by the magnitude of the electric field vector. The electric potential at a point r in a static electric field E is given by the line integral where C is an arbitrary path connecting the point with zero potential to r.

When the curl ∇ × E is zero, the line integral above does not depend on the specific path C chosen but only on its endpoints. In this case, the electric field is conservative and determined by the gradient of the potential: Then, by Gauss's law, the potential satisfies Poisson's equation: ∇ ⋅ E = ∇ ⋅ = − ∇ 2 V E = ρ / ε 0, where ρ is the total charge density and ∇· denotes the divergence; the concept of electric potential is linked with potential energy. A test charge q has an electric potential energy UE given by U E = q V; the potential energy and hence the electric potential is only defined up to an additive constant: one must arbitrarily choose a position where the potential energy and the electric potential are zero. These equations cannot be used if the curl ∇ × E ≠ 0, i.e. in the case of a non-conservative electric field. The generalization of electric potential to this case is described below; the electric potential arising from a point charge Q, at a distance r from the charge is observed to be V E = 1 4 π ε 0 Q r, where ε0 is the permittivity of vacuum.

V E is known as the Coulomb potential. The electric potential for a system of point charg

Austrocidaria lithurga

Austrocidaria lithurga is a species of moth in the family Geometridae. It is endemic to New Zealand; this moth is classified as at risk uncommon by the Department of Conservation. This species was first named Hydriomena lithurga. Meyrick used a specimen obtained from R. M. Sunley who had collected a pupa from a Muehlenbeckia plant at Makara Beach, Wellington, in November and had raised the adult in captivity. George Hudson described and illustrated the species in his 1928 book The Butterflies and Moths of New Zealand. In 1971 John S. Dugdale assigned H. lithurga to the genus Austrocidaria. Dugdale postulated; the holotype specimen is held at London. Meyrick described this species as follows: ♂︎. 25 mm. Head and thorax pale greyish-ochreous mixed with whitish, transversely barred with blackish-grey suffusion. Palpi ​1 1⁄2, blackish-grey, lower longitudinal half whitish. Antennae somewhat stout, shortly ciliated. Abdomen pale greyish-ochreous, mixed on sides with dark grey and whitish, segmental margins white preceded by a black mark on each side of back.

Forewings triangular, costa rather arched towards apex, apex obtuse, termen rather obliquely rounded, crenate. Hindwings with termen rounded, crenate; this species is endemic to New Zealand. This species range is Mid Canterbury; as well as the type locality, this species is recorded as having been collected at Sinclair Head and at Baring Head, both in Wellington. It has been located in south Marlborough, it is possible that the species is present at Little Bush, Puketitiri, in the Hawkes Bay. The pupa of this species is attached to a loose cocoon; the adult moth is on the wing in November. Hudson hypothesised that the host plants of the larvae of this moth are Muehlenbeckia species and it has been suggested that the host plants are divaricating small-leaved Coprosma species; however the precise host species for this moth is unknown as is its preferred habitat but it has been hypothesised that A. tithurga prefers open shrub-land. This moth is classified under the New Zealand Threat Classification System as being at risk uncommon.

Image of holotype specimen

Frank Jæger

Frank Jæger was a Danish writer most known for his poetry and radio plays. He received the Grand Prize of the Danish Academy in 1969, he edited two volumes of Heretica magazine with Tage Skou-Hansen. Jæger was born in the Frederiksberg district of Copenhagen on 19 June 1926, he graduated from Schneekloth's School in 1945 and from the Royal School of Library Science in 1950 but could by already make a living from his writings. Dydige digte Morgenens trompet De fem årstider Iners Hverdagshistorier Tune – det første år Den unge Jægers lidelser Tyren 19 Jægerviser Jomfruen fra Orléans, Jeanne d'Arc Havkarlens sange Kapellanen og andre fortællinger Til en følsom Veninde. Udvalgte digte Velkommen, Vinter og andre essays Hvilket postbud – en due Cinna og andre digte Digte 1953-59 Fyrre Digte Pastorale. Pelsen Drømmen om en sommerdag og andre Essays Danskere. Tre Fortællinger af Fædrelandets Historier Idylia Naive rejser Alvilda Årets ring Døden i skoven Essays gennem ti Aar Hjemkomst Stå op og tænd ild Udvalgte digte Provinser S Udsigt til Kronborg Danish Critics Prize for Literature De gyldne laurbær Emil Aarestrup Medaillen Søren Gyldendal Prize Grand Prize of the Danish Academy