Tiêu đề ELECTRONICS.pdf ✅

0 PHYSICS FORM SIX ELECTRONICS MsomiBora.com The Best Education Blog in Tanzania
1 ELECTRONICS It is the branch of science which deals with the electron flow through a vacuum, gas or semiconductor. Classification of substances on the basis of conduction of electricity. Solid We know that, each substance is composed of atoms. Substances are mainly classified into three categories namely solids, liquids and gases. In each solid atoms are at a definite positions and the average distance between them is constant. Depending upon the internal arrangement of atoms, solids are further divided into two groups. 1. Crystalline Solids The solid in which the atoms are arranged in a regular order are called the crystalline solids. In other words, we can say that in a crystalline solid. There is periodicity and regularity of its component atoms in all the directions. For example sodium chloride (common salt), diamond, Sugar, silver etc are the crystalline solids. Their atoms are arranged in a definite geometrical shape. They have a definite melting point. They are anisotropic, i.e., their physical properties such as thermal Conductivity refractive index etc, are different in different directions. They are the real solids. 2. Amorphous Solids The Solids in which the atoms do not have a definite arrangement are called the amorphous solids. They are also called the glassy solids. For example glass, rubber, plastic, power, etc are the amorphous solids. They do not have a definite arrangement of its atoms, i e., they do not have a characteristic geometrical shape. They do not have a definite melting point. They are isotropic. i.e., their physical properties such as conductivity of heat refractive index etc., are same in all the directions. They are not the real solids.
2 MONOCRYSTAL AND POLYCRYSTALLINE Monocrystal is a crystal in which the ordered arrangements of the atoms or molecules extends throughout the piece of solid, irrespective of its size. Polycrystal is a crystalline solid in which each piece of the solid has a number of monocrystals with developed faces joined together. The polycrystal ceramic made from PbO, ZnO and TiO are used in gas lighters and telephone receivers. Liquid Crystals Some organic crystalline solid when heated acquire fluidity but retain their anisotropic properties. They are called liquid crystals. Some liquid crystals like cyanbiphenyl can change the plane of polarization of light and such Liquid Crystal Displays (LCD) are used in watches and micro calculators. Crystal Lattice A crystal is made up of a three- dimensional array of points such that each point is surrounded by the height bouring POints in an identical way. Such an array of points is known as bravais lattice or space lattice. Unit cell is the smallest unit of the crystal lattice, repetition of which in three dimensions gives rise to crystal lattice. The length of three sides of a unit cell are called Primitives or lattice constant represented by a, b, c. The angle between three crystallographic axis are called interfacial angles represented by α, β and γ. The primitives and interfacial angles constitute the lattice parameters of a unit cell. [The cubic crystal may be of the form, simple cubic (sc) lattice, the body centred cubic (bee) lattice, the face centred Cubic (fcc) lattice.] The coordination number is defined as the number of nearest neighbours around any lattice point (or atom) in the crystal lattice. (a) For sc, coordination number is 6. (b) For bee, coordination number is 8. (c) For fcc, coordination number is 12. (d) For sc, atomic radius is a / 2.
3 (e) For bcc, atomic is a √3 / 4. (f) For fcc. atomic radius is a / 2√2. Classification of solids on the basis of conductivity (i) Conductor Conductors are those substances through which electricity can pass easily, e.g., all metals are conductors. (ii) Insulator Insulators are those substances through which electricity cannot pass, e.g., wood. rubber, mica etc. (iii) Semiconductor Semiconductors are those substances whose conductivity lies between conductors and insulators. e.g., germanium, silicon, carbon etc.