________________
3.
extends over a large volume of the crystal i.e. crystals exhibit a long range order of the atoms and molecules. Crystalline substances are bounded by flat sufraces. 4. Crystalline substances are anisotrophic i.e. the physical properties like thermal conductivity, electrical conductivity, compressibility, etc. have different values in different directions.
5.
Crystalline materials possess uniform chemical composition i.e. bonds between all the ions, atoms or molecules are of equal strength.
6.
A crystalline material has a sharp melting point. It is because, all the bonds between its constituents are of equal strength; and on heating, all the bonds get ruptured suddenly at a fixed temperature. Due to this, the change from solid state to the liquid state occurs suddenly.
7.
Below the temperature of crystallisation, the crystalline materials are in stable state. Since a stable state is the state of minimum energy, such a material acquires a state of minimum energy on crystallisation.
(ક) નક્કર પદાર્થ (ધાતુ)માં વાહકતા છે, એને સમજવા માટે અહીં ઉદ્ધૃત
છે
"Electron Emission
"The emission of electric charges from hot bodies constitutes thermionic emission. Edison discovered that current travels from a negative potential to positive potential through a vacuum. Structure of Solids :
a
According to present concepts, a metal is regarded as conglomerate of crystals. Within each crystal the atoms are held by interatomic forces in a regular pattern of space lattice. Each atom in turn consists of a nucleus surrounded by moving electrons travelling in well-defined orbits. Some of the electrons in the outer orbit of an atom are not rigidly bound to the atom, but are relatively free to travel more or less independently from one atom to the another. These are known as free electrons and it is these free electrons which are responsible for most of the electrical and in this chapter, we will study the effects associated with motion of electric charges. Moving charges constitute the electric currents.
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