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Electronics is study and use of circuitry involving such components as semi-conductors, thermionic valves and other vacuum devices, resistors, capacitors, and inductors.

Semi-conductor is a material, such as silicon or germanium that has a resistivity midway between that of conductors and that of insulators. In a pure semiconductor material, called an intrinsic semiconductor, the concentrations of negative charge carriers (electron) and positive charge carriers (holes) are the same. The conductivity increases considerably when certain impurities are added, depending strongly on the type and concentration of the impurity. Such a material is called an extrinsic semiconductor. The process of adding impurity to control the conductivity is called doping.

Diode is an electronic device with two electrodes that exhibits rectifying action when a potential difference is applied. Current flows for one direction of the potential (the forward direction) but when the potential is reversed the current is normally zero or very small.

Semi-conductor diode consists of a single p-n junction. The current across the junction increases exponentially with voltage in the forward direction, in the reverse direction there is only a very small (leakage) current until breakdown occurs.

Resistor is a component included in an electric circuit because of its resistance. Resistors may be variable or have a fixed value, they are made of resistance wire or carbon. Some types have a ceramic coating incorporating a colour coding in the form of stripes, which identify the value of the resistance.

Capacitor is a device for storing electric charge. It usually consists of two parallel conductors separated by some insulating material. The capacitance of a capacitor increases:

The greater the common area of the conductors

The smaller the distance between them

The higher the relative permittivity of the dielectric.

Opto-electronics is a subject or field that deals with the interaction of light with electronics. Many modern devices such as solar cells, lasers, photodetectors, optical fibres (fibre optics) etc. the modern technology and the future technology which will deals with the computers, space technology, medical science etc will be total or partially dependent on the field of Opto-electronics.