Tell about Electric Currents ?

on a metal surface subjected to a high electrical field. Vacuum tubes and sprytrons are some of the electronic switching and amplifying devices based on vacuum conducti

Chemical Effect Of Electric Current.

Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature.

The passage of an electric current through a conducting liquid causes chemical reactions.

It was discovered by Heike Kamerlingh Onnes on April 8, 1911 in Leiden

Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon.

The resulting effects are called chemical effects of currents.

. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state.

The process of depositing a layer of any desired metal on another material, by means of electricity, is called electroplating.

The occurrence of the Meissner effect indicates that superconductivity cannot be understood simply as the idealization of perfect conductivity in classical physics.

Main article: Semiconductor
In a semiconductor it is sometimes useful to think of the current as due to the flow of positive "holes

The heating element of the heater is made up of alloy which has very high resistance so when current flows through the heating element,

it becomes too hot and glows red.

holes" (the mobile positive charge carriers that are places where the semiconductor crystal is missing a valence electron).

the resistance of cord which is usually of copper or aluminium is very law so it does not glow.

This is the case in a p-type semiconductor. A semiconductor has electrical conductivity intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 10−2 to 104

In the classic crystalline semiconductors, electrons can have energies only within certain bands (i.e. ranges of levels of energy).

Energetically, these bands are located between the energy of the ground state, the state in which electrons are tightly bound to the atomic nuclei of the material, and the free electron energy, the latter describing the energy required for an electron to escape entirely from the material

The energy bands each correspond to a large number of discrete quantum states of the electrons, and most of the states with low energy (closer to the nucleus) are occupied, up to a particular band called the valence band.

Semiconductors and insulators are distinguished from metals because the valence band in any given metal is nearly filled with electrons under usual operating conditions, while very few (semiconductor) or virtually none (insulator) of them are available in the conduction band, the band immediately above the valence band.

The ease of exciting electrons in the semiconductor from the valence band to the conduction band depends on the band gap between the bands. The size of this energy band gap serves as an arbitrary dividing line (roughly 4 eV) between semiconductors and insulators.

With covalent bonds, an electron moves by hopping to a neighboring bond.

The Pauli exclusion principle requires that the electron be lifted into the higher anti-bonding state of that bond.

For delocalized states, for example in one dimension – that is in a nanowire, for every energy there is a state with electrons flowing in one direction and another state with the electrons flowing in the other

For a net current to flow, more states for one direction than for the other direction must be occupied. For this to occur, energy is required, as in the semiconductor the next higher states lie above the band gap. Often this is stated as: