Category : JEE Main & Advanced
Some of the properties of solids which are useful in electronic and magnetic devices such as, transistor, computers, and telephones etc., are summarised below, (1) Electrical properties : Solids are classified into following classes depending on the extent of conducting nature. (i) Conductors : The solids which allow the electric current to pass through them are called conductors. These are further of two types; Metallic conductors and electrolytic conductors. The electrical conductivity of these solids is high in the range \[{{10}^{4}}-{{10}^{6}}oh{{m}^{-1}}c{{m}^{-1}}\]. Their conductance decrease with increase in temperature. (ii) Insulators : The solids which do not allow the current to pass through them are called insulators. e.g., rubber, wood and plastic etc. the electrical conductivity of these solids is very low i.e., \[{{10}^{-12}}-{{10}^{-22}}oh{{m}^{-1}}c{{m}^{-1}}\]. (iii) Semiconductors : The solids whose electrical conductivity lies between those of conductors and insulators are called semiconductors. The conductivity of these solid is due to the presence of impurities. e.g. Silicon and Germanium. Their conductance increase with increase in temperature. The electrical conductivity of these solids is increased by adding impurity. This is called Doping. When silicon is doped with P (or As, group 5th elements), we get n-type semiconductor. This is because P has five valence electrons. It forms 4 covalent bonds with silicon and the fifth electron remains free and is loosely bound. This give rise to n-type semiconductor because current is carried by electrons when silicon is doped with Ga (or in In/Al, group 3rd elements) we get p-type semiconductors. Superconductivity : When any material loses its resistance for electric current, then it is called superconductor, Kammerlingh Onnes (1913) observed this phenomenon at 4K in mercury. The materials offering no resistance to the flow of current at very low temperature (2-5K) are called superconducting materials and phenomenon is called superconductivity. Examples, \[N{{b}_{3}}\]Ge alloy (Before 1986) \[L{{a}_{1.25}}B{{a}_{0.15}}Cu{{O}_{4}}\] (1986) \[YB{{a}_{2}}\]\[C{{u}_{3}}{{O}_{7}}\] (1987) Following are the important applications of superconductivity, (a) Electronics, (b) Building supermagnets, (c) Aviation transportation, (d) Power transmission ?The temperature at which a material enters the superconducting state is called the superconducting transition temperature, \[({{T}_{c}})\]?. Superconductivity was also observed in lead (Pb) at 7.2 K and in tin (Sn) at 3.7K. The phenomenon of superconductivity in other materials such as polymers and organic crystals. Examples are (SN)x, polythiazyl, the subscript x indicates a large number of variable size. (TMTSF)2PF6, where TMTSF is tetra methyl tetra selena fulvalene. (2) Magnetic properties : Based on the behavior of substances when placed in the magnetic field, there are classified into five classes. Magnetic properties of solids
Properties | Description | Alignment of Magnetic Dipoles | Examples | Applications |
Diamagnetic | Feebly repelled by the magnetic fields. Non-metallic elements (excepts O2, S) inert gases and species with paired electrons are diamagnetic | All paired electrons | TiO2, V2O5, NaCl, C6H6 (benzene) | Insulator |
Paramagnetic | Attracted by the magnetic field due to the presence of permanent magnetic dipoles (unpaired electrons). In magnetic field, these tend to orient themselves parallel to the direction of the field and thus, produce magnetism in the substances. | At least one unpaired electron | \[{{O}_{2}},\,C{{u}^{2+}},\,F{{e}^{3+}},\,TiO,\] \[T{{i}_{2}}{{O}_{3}},\,VO,\,V{{O}_{2}}\], CuO | Electronic appliances |
Ferromagnetic | Permanent magnetism even in the absence of magnetic field, Above a temperature called Curie temperature, there is no ferromagnetism. | Dipoles are aligned in the same direction | Fe, Ni, Co, CrO2 | CrO2 is used in audio and video tapes |
Antiferromagnetic | This arises when the dipole alignment is zero due to equal and opposite alignment. | MnO, MnO2, Mn2O, FeO, Fe2O3; NiO, Cr2O3, CoO, Co3O4, | ? | |
Ferrimagnetic | This arises when there is net dipole moment | Fe3O4, ferrites | ? |
You need to login to perform this action.
You will be redirected in
3 sec