{"id":215,"date":"2018-11-15T08:43:46","date_gmt":"2018-11-15T08:43:46","guid":{"rendered":"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/?post_type=chapter&#038;p=215"},"modified":"2018-11-15T12:27:21","modified_gmt":"2018-11-15T12:27:21","slug":"tensors","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/chapter\/tensors\/","title":{"rendered":"Tensors"},"content":{"raw":"<div>\r\n<p style=\"text-align: justify\"><strong>TABLE OF CONTENTS<\/strong><\/p>\r\n<p style=\"text-align: justify\">1. Rotation and vectors<\/p>\r\n<p style=\"text-align: justify\">2. The tensor notation<\/p>\r\n<p style=\"padding-left: 30px;text-align: justify\">2.1 Einstein summation convention<\/p>\r\n<p style=\"text-align: justify\">3.\u00a0 Matrix representation<\/p>\r\n<p style=\"text-align: justify\">4.\u00a0 Rotations and tensors<\/p>\r\n<p style=\"padding-left: 30px;text-align: justify\">4.1 Pseudo-tensors<\/p>\r\n<p style=\"text-align: justify\">5. Playing with indices<\/p>\r\n<p style=\"padding-left: 30px;text-align: justify\">5.1 The Kronecker delta and permutation symbol<\/p>\r\n<p style=\"text-align: justify\">6.\u00a0 Vector identities<\/p>\r\n<p style=\"text-align: justify\">7.\u00a0 The Kronecker delta and permutation symbol as tensors<\/p>\r\n<p style=\"padding-left: 30px;text-align: justify\">7.1 Isotropic tensors<\/p>\r\n<p style=\"padding-left: 30px;text-align: justify\">7.2 Physical significance of isotropic tensor of rank two<\/p>\r\n\r\n<\/div>\r\n&nbsp;\r\n\r\n<strong style=\"text-align: initial;font-size: 1em\">LEARNING OBJECTIVES<\/strong>\r\n<div>\r\n<p style=\"text-align: justify\">\u00a0 \u00a01. In this module a new perspective is given to the idea of vectors which are related to properties of physical quantities under rotation.<\/p>\r\n<p style=\"text-align: justify\">2. The tensor notation is introduced which is a big help in this study of rotational properties.<\/p>\r\n<p style=\"text-align: justify\">3. Next the Einstein summation convention which simplifies the formalism is introduced.<\/p>\r\n<p style=\"text-align: justify\">4. Vectors are defined from the perspective of their properties under rotation in the three dimensional physical space. The idea is then generalized to tensors of second and higher order ranks.<\/p>\r\n<p style=\"text-align: justify\">5. Further classification of physical quantities on the basis of their behaviour under inversion of the coordinate axes is also discussed.<\/p>\r\n<p style=\"text-align: justify\">6. In this tensor (or index) notation the indices play a very important role and it is demonstrated how playing around with indices leads to many significant results.<\/p>\r\n<p style=\"text-align: justify\">7. Two very special tensors, the Kronecker delta and the permutation tensor are introduced and their properties discussed in detail.<\/p>\r\n<p style=\"text-align: justify\">8. Next certain vector identities are written down and it is demonstrated how the tensor methods greatly simplify the derivation of such identities.<\/p>\r\n<p style=\"text-align: justify\">9. Next it is proved that Kronecker delta and the permutation tensor are indeed tensors of rank two and three respectively.<\/p>\r\n<p style=\"text-align: justify\">10. The idea of isotropic tensors is briefly introduced and isotropic tensors of rank up to four described.<\/p>\r\n\r\n<\/div>\r\n&nbsp;\r\n<p style=\"text-align: center\"><strong style=\"text-align: initial;font-size: 1em\">T e n s o r s<\/strong><\/p>\r\n\r\n<div>\r\n\r\n&nbsp;\r\n\r\n<span style=\"text-decoration: underline\"><strong>1. Rotations and Vectors<\/strong><\/span>\r\n\r\n&nbsp;\r\n<p style=\"text-align: justify\">So far we have studied two kinds of physical quantities; scalars which need only a magnitude to describe them, and vectors which, in addition, need a direction to specify them completely. There are many physical entities that do not fall in either of these two categories. They require more than one direction to specify them, so to say. We now wish to generalize our ideas to include such objects in our study as well. For that purpose we first reintroduce vectors from another point of view, viz., through their transformation properties under rotations in the physical three dimensional space. This is a more satisfactory way to introduce vectors than simply as objects having both magnitude and direction. This definition can then be easily generalized to include other physical entities that we have in mind.<\/p>\r\n<img class=\"alignnone wp-image-218 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-60.png\" alt=\"\" width=\"800\" height=\"443\" \/>\r\n\r\n<\/div>\r\n<div>\r\n<p style=\"padding-left: 30px\"><span style=\"text-decoration: underline\"><strong>2. The tensor notation<\/strong><\/span><\/p>\r\n<img class=\"alignnone wp-image-219 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-61.png\" alt=\"\" width=\"848\" height=\"156\" \/>\r\n\r\n<\/div>\r\n<div>\r\n\r\n<img class=\"alignnone wp-image-220 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-62.png\" alt=\"\" width=\"862\" height=\"416\" \/>\r\n<p style=\"text-align: justify\">Together these equations can be written as<\/p>\r\n<img class=\"wp-image-221 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-63.png\" alt=\"\" width=\"587\" height=\"63\" \/>\r\n\r\n<\/div>\r\n<img class=\"alignnone wp-image-222 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-64.png\" alt=\"\" width=\"856\" height=\"413\" \/>\r\n<div><\/div>\r\n<span style=\"text-align: initial;font-size: 1em\">Hence<\/span>\r\n\r\n<img class=\"size-full wp-image-223 aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-65.png\" alt=\"\" width=\"240\" height=\"60\" \/>\r\n\r\n<img class=\"wp-image-224 alignnone\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-66.png\" alt=\"\" width=\"798\" height=\"29\" \/><span style=\"text-align: initial;font-size: 1em\">On comparing the coefficients of various terms we have<\/span>\r\n\r\n<img class=\"alignnone wp-image-225 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-67.png\" alt=\"\" width=\"794\" height=\"311\" \/>\r\n<div>\r\n<p style=\"padding-left: 30px\"><strong>2.1 Einstein summation convention<\/strong><\/p>\r\n<p style=\"padding-left: 30px;text-align: justify\">The notation and writing can be further simplified by using what is called the <em>Einstein summation convention<\/em>. Under this convention<\/p>\r\n\r\n<ul>\r\n \t<li style=\"text-align: justify\">An index (subscript) can appear <strong>only once or twice<\/strong>.\u00a0 Each index take values (<em>1, 2, 3<\/em>)<\/li>\r\n \t<li style=\"text-align: justify\">An index that appears once is a <em>free index<\/em>. Every free index represents a set of three equations for three values of the index.<\/li>\r\n \t<li style=\"text-align: justify\">An index that appears twice is a <em>dummy index.<\/em> The index is understood to be summed over, so that every such index represents a sum of three terms.<\/li>\r\n \t<li style=\"text-align: justify\">One dummy index can be freely replaced by another. Thus<\/li>\r\n<\/ul>\r\n<img class=\"alignnone size-full wp-image-226 aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-68.png\" alt=\"\" width=\"299\" height=\"57\" \/>\r\n<ul>\r\n \t<li style=\"text-align: justify\">The free indices must match on the two sides of an equation and on each term of an expression.<\/li>\r\n<\/ul>\r\n<img class=\"alignnone wp-image-228 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-70.png\" alt=\"\" width=\"863\" height=\"98\" \/>\r\n\r\n<\/div>\r\n<div>\r\n\r\n<img class=\"alignnone wp-image-229 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-71.png\" alt=\"\" width=\"717\" height=\"324\" \/>\r\n\r\n<\/div>\r\n<div>\r\n<p style=\"padding-left: 30px\"><span style=\"text-decoration: underline\"><strong><span style=\"text-align: initial;font-size: 1em\">3. Matrix representation<\/span><\/strong><\/span><\/p>\r\n<p style=\"padding-left: 30px;text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Many of the equations <\/span><span style=\"text-align: initial;font-size: 1em\">above can be written in an even simpler form in terms of matrices. <\/span><span style=\"text-align: initial;font-size: 1em\">If we put the\u00a0<\/span><span style=\"text-align: initial;font-size: 1em\">coordinates of a point in\u00a0<\/span><span style=\"text-align: initial;font-size: 1em\">the form of a column matrix.<\/span><\/p>\r\n<img class=\"alignnone wp-image-230 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-72.png\" alt=\"\" width=\"720\" height=\"416\" \/>\r\n\r\n<\/div>\r\n<div><\/div>\r\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">\u00a0 The symbol <\/span><em style=\"text-align: initial;font-size: 1em\">x<\/em><span style=\"text-align: initial;font-size: 1em\"> is being used for the set of three coordinates and not for the abstract vector which it represents. The superscript (<\/span><em style=\"text-align: initial;font-size: 1em\">T<\/em><span style=\"text-align: initial;font-size: 1em\">) refers to the transpose of a matrix and <\/span><em style=\"text-align: initial;font-size: 1em\">I<\/em><span style=\"text-align: initial;font-size: 1em\"> refers to the unit matrix. The matrix <\/span><em style=\"text-align: initial;font-size: 1em\">a<\/em><span style=\"text-align: initial;font-size: 1em\"> is such that<\/span><\/p>\r\n<img class=\"wp-image-231 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-73.png\" alt=\"\" width=\"589\" height=\"37\" \/>\r\n<div><\/div>\r\n<div>\r\n<p style=\"text-align: justify\">\u00a0 A matrix with this property is called an <em>orthogonal matrix<\/em>.\u00a0 Thus rotation is represented by an orthogonal matrix. This in fact is true not only in two or three dimensions but for rotations in any dimensions.<\/p>\r\n<p style=\"text-align: justify\"><img class=\"alignnone wp-image-232 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-74.png\" alt=\"\" width=\"809\" height=\"158\" \/>\u00a0 \u00a0<span style=\"text-align: initial;font-size: 1em\">Thus the inverse transformation is given by the transpose of the coefficients.<\/span><\/p>\r\n\r\n<\/div>\r\n<div>\r\n<p style=\"padding-left: 30px\"><span style=\"text-decoration: underline\"><strong>4. Rotations and tensors<\/strong><\/span><\/p>\r\n&nbsp;\r\n<p style=\"text-align: justify\">So far we have studied the properties of the position vector under rotations. We now extend the same ideas to other physical quantities and thereby define tensors of second and higher ranks as physical quantities having more complicated transformation properties under rotations.<\/p>\r\n&nbsp;\r\n\r\nWe first redefine a vector in terms of its transformation properties under rotations. The position vector transforms according to the equation\r\n\r\n<img class=\"wp-image-233 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-75.png\" alt=\"\" width=\"592\" height=\"39\" \/>\r\n\r\n<img class=\"alignnone wp-image-234 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-76.png\" alt=\"\" width=\"811\" height=\"118\" \/>\r\n\r\n<img class=\"wp-image-235 size-full alignnone\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-77.png\" alt=\"\" width=\"703\" height=\"79\" \/>\r\n\r\n<span style=\"text-align: initial;font-size: 1em\">Every physical quantity cannot be categorized as belonging to the set of scalars and vectors. There are others that transform in a more complicated way under rotations. Any set of nine physical quantities which transforms in the following way under rotations are said to form a <\/span><em style=\"text-align: initial;font-size: 1em\">tensor of rank two:<\/em>\r\n\r\n<img class=\"wp-image-236 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-78.png\" alt=\"\" width=\"525\" height=\"34\" \/>\r\n\r\n<\/div>\r\n<div>\r\n\r\n<span style=\"text-align: initial;font-size: 1em\">\u00a0 \u00a0 Moment of inertia, stress and strain, and Maxwell\u2019s stress tensor are all examples of tensors of rank two. Vectors can be regarded as <\/span><em style=\"text-align: initial;font-size: 1em\">tensors of rank one<\/em><span style=\"text-align: initial;font-size: 1em\"> and scalars as <\/span><em style=\"text-align: initial;font-size: 1em\">tensors of rank zero<\/em><span style=\"text-align: initial;font-size: 1em\">.<\/span>\r\n\r\n<\/div>\r\n<span style=\"text-align: initial;font-size: 1em\"><img class=\"alignnone wp-image-237 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-79.png\" alt=\"\" width=\"853\" height=\"104\" \/><\/span>\r\n<div>\r\n<p style=\"padding-left: 30px\"><strong>4.1 Pseudo Tensors<\/strong><\/p>\r\n\r\n<\/div>\r\n<div>\r\n\r\nCertain further properties of the transformation coefficients are interesting. Let us take the determinant of both sides of equation (16)\r\n\r\n<img class=\"wp-image-238 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-80.png\" alt=\"\" width=\"589\" height=\"39\" \/>\r\n\r\nNow for the identity transformation, det(<em>a<\/em>)=1. Since rotation is a continuous transformation, under any rotation det(<em>a<\/em>) will change continuously. Since det(<em>a<\/em>) is allowed only two values, +1 or -1, <em>det(a)=1 under any<\/em> <em>continuous rotation<\/em>. On the other hand for a reflection in a plane, say the<em> z=0 <\/em>plane, we have\r\n\r\n<img class=\"size-full wp-image-239 aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-81.png\" alt=\"\" width=\"189\" height=\"33\" \/>\r\n\r\n<\/div>\r\n<div>\r\n\r\nThis is represented by the transformation matrix\r\n\r\n<img class=\"wp-image-240 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-82.png\" alt=\"\" width=\"631\" height=\"110\" \/>\r\n\r\n<span style=\"text-align: initial;font-size: 1em\">The same is true of inversion in three dimensions Based on this we have the following results<\/span>\r\n\r\n<img class=\"alignnone wp-image-241 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-83.png\" alt=\"\" width=\"811\" height=\"454\" \/>\r\n\r\n<\/div>\r\n<div>\r\n<p style=\"padding-left: 60px\"><span style=\"text-decoration: underline\"><strong>5.\u00a0 Playing with indices<\/strong><\/span><\/p>\r\n<img class=\"alignnone wp-image-242 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-84.png\" alt=\"\" width=\"499\" height=\"33\" \/>\r\n\r\n<\/div>\r\n<div><\/div>\r\n<img class=\"alignnone wp-image-243 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-85.png\" alt=\"\" width=\"867\" height=\"532\" \/>\r\n<div>\r\n<p style=\"padding-left: 30px\"><strong>5.1 The Kronecker delta and permutation symbol<\/strong><\/p>\r\n<img class=\"alignnone wp-image-244 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-86.png\" alt=\"\" width=\"805\" height=\"363\" \/>\r\n\r\n<\/div>\r\n<div>\r\n\r\n<img class=\"alignnone wp-image-245 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-87.png\" alt=\"\" width=\"859\" height=\"444\" \/>\r\n\r\n<img class=\"alignnone wp-image-246 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-88.png\" alt=\"\" width=\"811\" height=\"173\" \/>\r\n\r\n<img class=\"alignnone wp-image-248 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-90.png\" alt=\"\" width=\"764\" height=\"342\" \/>\r\n\r\n<img class=\"alignnone wp-image-249 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-91.png\" alt=\"\" width=\"804\" height=\"342\" \/>\r\n\r\n<\/div>\r\n<div>\r\n<p style=\"padding-left: 60px\"><span style=\"text-decoration: underline\"><strong>6. Vector Identities<\/strong><\/span><\/p>\r\n<p style=\"text-align: justify\">Many of the vector relations can be proved more conveniently by using the \u201ctensor notation\u201d. Let us, as an example, consider<\/p>\r\n<img class=\"wp-image-250 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-92.png\" alt=\"\" width=\"585\" height=\"52\" \/>\r\n\r\n<\/div>\r\n<div>\r\n\r\nTo use the \u201ctensor methods\u201d to prove this relation, let us find the <em>i<\/em>th component of left hand side:\r\n\r\n<img class=\"alignnone wp-image-251 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-93.png\" alt=\"\" width=\"800\" height=\"195\" \/>\r\n\r\n&nbsp;\r\n\r\n&nbsp;\r\n\r\n&nbsp;\r\n\r\n<strong>The differential operator as a tensor<\/strong>\r\n\r\nThe differential operators can obviously also be written in the tensor notation. Thus we have\r\n\r\n<img class=\"alignnone size-full wp-image-252\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-94.png\" alt=\"\" width=\"279\" height=\"219\" \/>\r\n\r\n<img class=\"alignnone wp-image-253 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-95.png\" alt=\"\" width=\"807\" height=\"264\" \/>\r\n\r\n<\/div>\r\n<div>\r\n<p style=\"padding-left: 30px\"><span style=\"text-decoration: underline\"><strong>7. The Kronecker delta and permutation symbol as tensors<\/strong><\/span><\/p>\r\n<p style=\"text-align: justify\">We have so far defined Kronecker delta and permutation symbol as simply that, as objects having specific components. But these are indeed tensors in the sense that they have the required transformation properties under rotations. On using equations (13) and (22) we have<\/p>\r\n<img class=\"alignnone wp-image-254 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-96.png\" alt=\"\" width=\"812\" height=\"363\" \/>\r\n\r\n&nbsp;\r\n\r\n<strong>7.1 Isotropic tensors<\/strong>\r\n\r\nAn isotropic tensor is one that has the same components in all rotated frames of reference, i.e.,\r\n\r\n<img class=\"size-full wp-image-255 aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-97.png\" alt=\"\" width=\"135\" height=\"42\" \/>\r\n\r\nWe can classify isotropic tensors as follows:\r\n\r\n<img class=\"alignnone wp-image-256 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-98.png\" alt=\"\" width=\"770\" height=\"54\" \/>\r\n\r\n<img class=\"alignnone wp-image-257 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-99.png\" alt=\"\" width=\"579\" height=\"126\" \/>\r\n\r\n<img class=\"alignnone wp-image-259 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-101.png\" alt=\"\" width=\"812\" height=\"451\" \/>\r\n\r\n<img class=\"alignnone wp-image-260 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-102.png\" alt=\"\" width=\"802\" height=\"137\" \/>\r\n\r\n<\/div>\r\n<div>\r\n<p style=\"padding-left: 30px\"><strong>7.2 Physical significance of isotropic tensor of rank two<\/strong><\/p>\r\nAn isotropic tensor behaves much like a scalar. Consider for example the conductivity tensor. In an anisotropic medium the relation between the electric field and the current density takes the form\r\n\r\n<img class=\"size-full wp-image-261 aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-103.png\" alt=\"\" width=\"98\" height=\"31\" \/>\r\n\r\n<img class=\"alignnone wp-image-262 \" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-104.png\" alt=\"\" width=\"809\" height=\"100\" \/>\r\n\r\n<\/div>\r\n<div>\r\n<p style=\"padding-left: 30px\"><img class=\"alignnone wp-image-263 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-105.png\" alt=\"\" width=\"853\" height=\"244\" \/><\/p>\r\n\r\n<\/div>\r\n<p style=\"padding-left: 30px\"><strong>SUMMARY<\/strong><\/p>\r\n\r\n<ul>\r\n \t<li>In this module we develop a new perspective for the idea of vectors which are related to properties of physical quantities under rotation.<\/li>\r\n \t<li>We introduce the so called tensor notation which is a big help in this study of rotational properties.<\/li>\r\n \t<li>Next we introduce and explain with examples the Einstein summation convention which simplifies the formalism even further.<\/li>\r\n \t<li>We then define vectors from this new perspective of properties of physical quantities under rotations in the three dimensional physical space. We then generalize the idea to tensors of second and higher order ranks and explain how scalars and vectors are tensors of rank zero and one respectively.<\/li>\r\n \t<li>Next we further classify physical quantities on the basis of their behaviour under inversion of the coordinate axes and introduce true and pseudo tensors.<\/li>\r\n \t<li>In this tensor (or index) notation the indices play a very important role and we demonstrate how playing around with indices leads to many significant results.<\/li>\r\n \t<li>Next we formally introduce two very special tensors, the Kronecker delta and the permutation tensor and discuss their usefulness and properties.<\/li>\r\n \t<li>Next we write down certain vector identities and demonstrate how the tensor methods greatly simplify the derivation of such identities.<\/li>\r\n \t<li>Next we prove that Kronecker delta and the permutation tensor that were introduced are indeed tensors of rank two and three respectively.<\/li>\r\n \t<li>Finally we briefly discuss the idea of isotropic tensors and describe isotropic tensors of rank up to four.<\/li>\r\n<\/ul>","rendered":"<div>\n<p style=\"text-align: justify\"><strong>TABLE OF CONTENTS<\/strong><\/p>\n<p style=\"text-align: justify\">1. Rotation and vectors<\/p>\n<p style=\"text-align: justify\">2. The tensor notation<\/p>\n<p style=\"padding-left: 30px;text-align: justify\">2.1 Einstein summation convention<\/p>\n<p style=\"text-align: justify\">3.\u00a0 Matrix representation<\/p>\n<p style=\"text-align: justify\">4.\u00a0 Rotations and tensors<\/p>\n<p style=\"padding-left: 30px;text-align: justify\">4.1 Pseudo-tensors<\/p>\n<p style=\"text-align: justify\">5. Playing with indices<\/p>\n<p style=\"padding-left: 30px;text-align: justify\">5.1 The Kronecker delta and permutation symbol<\/p>\n<p style=\"text-align: justify\">6.\u00a0 Vector identities<\/p>\n<p style=\"text-align: justify\">7.\u00a0 The Kronecker delta and permutation symbol as tensors<\/p>\n<p style=\"padding-left: 30px;text-align: justify\">7.1 Isotropic tensors<\/p>\n<p style=\"padding-left: 30px;text-align: justify\">7.2 Physical significance of isotropic tensor of rank two<\/p>\n<\/div>\n<p>&nbsp;<\/p>\n<p><strong style=\"text-align: initial;font-size: 1em\">LEARNING OBJECTIVES<\/strong><\/p>\n<div>\n<p style=\"text-align: justify\">\u00a0 \u00a01. In this module a new perspective is given to the idea of vectors which are related to properties of physical quantities under rotation.<\/p>\n<p style=\"text-align: justify\">2. The tensor notation is introduced which is a big help in this study of rotational properties.<\/p>\n<p style=\"text-align: justify\">3. Next the Einstein summation convention which simplifies the formalism is introduced.<\/p>\n<p style=\"text-align: justify\">4. Vectors are defined from the perspective of their properties under rotation in the three dimensional physical space. The idea is then generalized to tensors of second and higher order ranks.<\/p>\n<p style=\"text-align: justify\">5. Further classification of physical quantities on the basis of their behaviour under inversion of the coordinate axes is also discussed.<\/p>\n<p style=\"text-align: justify\">6. In this tensor (or index) notation the indices play a very important role and it is demonstrated how playing around with indices leads to many significant results.<\/p>\n<p style=\"text-align: justify\">7. Two very special tensors, the Kronecker delta and the permutation tensor are introduced and their properties discussed in detail.<\/p>\n<p style=\"text-align: justify\">8. Next certain vector identities are written down and it is demonstrated how the tensor methods greatly simplify the derivation of such identities.<\/p>\n<p style=\"text-align: justify\">9. Next it is proved that Kronecker delta and the permutation tensor are indeed tensors of rank two and three respectively.<\/p>\n<p style=\"text-align: justify\">10. The idea of isotropic tensors is briefly introduced and isotropic tensors of rank up to four described.<\/p>\n<\/div>\n<p>&nbsp;<\/p>\n<p style=\"text-align: center\"><strong style=\"text-align: initial;font-size: 1em\">T e n s o r s<\/strong><\/p>\n<div>\n<p>&nbsp;<\/p>\n<p><span style=\"text-decoration: underline\"><strong>1. Rotations and Vectors<\/strong><\/span><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">So far we have studied two kinds of physical quantities; scalars which need only a magnitude to describe them, and vectors which, in addition, need a direction to specify them completely. There are many physical entities that do not fall in either of these two categories. They require more than one direction to specify them, so to say. We now wish to generalize our ideas to include such objects in our study as well. For that purpose we first reintroduce vectors from another point of view, viz., through their transformation properties under rotations in the physical three dimensional space. This is a more satisfactory way to introduce vectors than simply as objects having both magnitude and direction. This definition can then be easily generalized to include other physical entities that we have in mind.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-218\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-60.png\" alt=\"\" width=\"800\" height=\"443\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-60.png 686w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-60-300x166.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-60-65x36.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-60-225x125.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-60-350x194.png 350w\" sizes=\"auto, (max-width: 800px) 100vw, 800px\" \/><\/p>\n<\/div>\n<div>\n<p style=\"padding-left: 30px\"><span style=\"text-decoration: underline\"><strong>2. The tensor notation<\/strong><\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-219 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-61.png\" alt=\"\" width=\"848\" height=\"156\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-61.png 848w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-61-300x55.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-61-768x141.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-61-65x12.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-61-225x41.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-61-350x64.png 350w\" sizes=\"auto, (max-width: 848px) 100vw, 848px\" \/><\/p>\n<\/div>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-220 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-62.png\" alt=\"\" width=\"862\" height=\"416\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-62.png 862w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-62-300x145.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-62-768x371.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-62-65x31.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-62-225x109.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-62-350x169.png 350w\" sizes=\"auto, (max-width: 862px) 100vw, 862px\" \/><\/p>\n<p style=\"text-align: justify\">Together these equations can be written as<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-221 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-63.png\" alt=\"\" width=\"587\" height=\"63\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-63.png 587w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-63-300x32.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-63-65x7.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-63-225x24.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-63-350x38.png 350w\" sizes=\"auto, (max-width: 587px) 100vw, 587px\" \/><\/p>\n<\/div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-222 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-64.png\" alt=\"\" width=\"856\" height=\"413\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-64.png 856w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-64-300x145.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-64-768x371.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-64-65x31.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-64-225x109.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-64-350x169.png 350w\" sizes=\"auto, (max-width: 856px) 100vw, 856px\" \/><\/p>\n<div><\/div>\n<p><span style=\"text-align: initial;font-size: 1em\">Hence<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-223 aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-65.png\" alt=\"\" width=\"240\" height=\"60\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-65.png 240w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-65-65x16.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-65-225x56.png 225w\" sizes=\"auto, (max-width: 240px) 100vw, 240px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-224 alignnone\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-66.png\" alt=\"\" width=\"798\" height=\"29\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-66.png 851w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-66-300x11.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-66-768x28.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-66-65x2.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-66-225x8.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-66-350x13.png 350w\" sizes=\"auto, (max-width: 798px) 100vw, 798px\" \/><span style=\"text-align: initial;font-size: 1em\">On comparing the coefficients of various terms we have<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-225\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-67.png\" alt=\"\" width=\"794\" height=\"311\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-67.png 874w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-67-300x117.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-67-768x301.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-67-65x25.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-67-225x88.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-67-350x137.png 350w\" sizes=\"auto, (max-width: 794px) 100vw, 794px\" \/><\/p>\n<div>\n<p style=\"padding-left: 30px\"><strong>2.1 Einstein summation convention<\/strong><\/p>\n<p style=\"padding-left: 30px;text-align: justify\">The notation and writing can be further simplified by using what is called the <em>Einstein summation convention<\/em>. Under this convention<\/p>\n<ul>\n<li style=\"text-align: justify\">An index (subscript) can appear <strong>only once or twice<\/strong>.\u00a0 Each index take values (<em>1, 2, 3<\/em>)<\/li>\n<li style=\"text-align: justify\">An index that appears once is a <em>free index<\/em>. Every free index represents a set of three equations for three values of the index.<\/li>\n<li style=\"text-align: justify\">An index that appears twice is a <em>dummy index.<\/em> The index is understood to be summed over, so that every such index represents a sum of three terms.<\/li>\n<li style=\"text-align: justify\">One dummy index can be freely replaced by another. Thus<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-226 aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-68.png\" alt=\"\" width=\"299\" height=\"57\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-68.png 299w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-68-65x12.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-68-225x43.png 225w\" sizes=\"auto, (max-width: 299px) 100vw, 299px\" \/><\/p>\n<ul>\n<li style=\"text-align: justify\">The free indices must match on the two sides of an equation and on each term of an expression.<\/li>\n<\/ul>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-228 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-70.png\" alt=\"\" width=\"863\" height=\"98\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-70.png 863w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-70-300x34.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-70-768x87.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-70-65x7.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-70-225x26.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-70-350x40.png 350w\" sizes=\"auto, (max-width: 863px) 100vw, 863px\" \/><\/p>\n<\/div>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-229 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-71.png\" alt=\"\" width=\"717\" height=\"324\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-71.png 717w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-71-300x136.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-71-65x29.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-71-225x102.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-71-350x158.png 350w\" sizes=\"auto, (max-width: 717px) 100vw, 717px\" \/><\/p>\n<\/div>\n<div>\n<p style=\"padding-left: 30px\"><span style=\"text-decoration: underline\"><strong><span style=\"text-align: initial;font-size: 1em\">3. Matrix representation<\/span><\/strong><\/span><\/p>\n<p style=\"padding-left: 30px;text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">Many of the equations <\/span><span style=\"text-align: initial;font-size: 1em\">above can be written in an even simpler form in terms of matrices. <\/span><span style=\"text-align: initial;font-size: 1em\">If we put the\u00a0<\/span><span style=\"text-align: initial;font-size: 1em\">coordinates of a point in\u00a0<\/span><span style=\"text-align: initial;font-size: 1em\">the form of a column matrix.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-230 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-72.png\" alt=\"\" width=\"720\" height=\"416\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-72.png 720w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-72-300x173.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-72-65x38.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-72-225x130.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-72-350x202.png 350w\" sizes=\"auto, (max-width: 720px) 100vw, 720px\" \/><\/p>\n<\/div>\n<div><\/div>\n<p style=\"text-align: justify\"><span style=\"text-align: initial;font-size: 1em\">\u00a0 The symbol <\/span><em style=\"text-align: initial;font-size: 1em\">x<\/em><span style=\"text-align: initial;font-size: 1em\"> is being used for the set of three coordinates and not for the abstract vector which it represents. The superscript (<\/span><em style=\"text-align: initial;font-size: 1em\">T<\/em><span style=\"text-align: initial;font-size: 1em\">) refers to the transpose of a matrix and <\/span><em style=\"text-align: initial;font-size: 1em\">I<\/em><span style=\"text-align: initial;font-size: 1em\"> refers to the unit matrix. The matrix <\/span><em style=\"text-align: initial;font-size: 1em\">a<\/em><span style=\"text-align: initial;font-size: 1em\"> is such that<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-231 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-73.png\" alt=\"\" width=\"589\" height=\"37\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-73.png 589w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-73-300x19.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-73-65x4.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-73-225x14.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-73-350x22.png 350w\" sizes=\"auto, (max-width: 589px) 100vw, 589px\" \/><\/p>\n<div><\/div>\n<div>\n<p style=\"text-align: justify\">\u00a0 A matrix with this property is called an <em>orthogonal matrix<\/em>.\u00a0 Thus rotation is represented by an orthogonal matrix. This in fact is true not only in two or three dimensions but for rotations in any dimensions.<\/p>\n<p style=\"text-align: justify\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-232\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-74.png\" alt=\"\" width=\"809\" height=\"158\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-74.png 849w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-74-300x59.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-74-768x150.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-74-65x13.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-74-225x44.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-74-350x68.png 350w\" sizes=\"auto, (max-width: 809px) 100vw, 809px\" \/>\u00a0 \u00a0<span style=\"text-align: initial;font-size: 1em\">Thus the inverse transformation is given by the transpose of the coefficients.<\/span><\/p>\n<\/div>\n<div>\n<p style=\"padding-left: 30px\"><span style=\"text-decoration: underline\"><strong>4. Rotations and tensors<\/strong><\/span><\/p>\n<p>&nbsp;<\/p>\n<p style=\"text-align: justify\">So far we have studied the properties of the position vector under rotations. We now extend the same ideas to other physical quantities and thereby define tensors of second and higher ranks as physical quantities having more complicated transformation properties under rotations.<\/p>\n<p>&nbsp;<\/p>\n<p>We first redefine a vector in terms of its transformation properties under rotations. The position vector transforms according to the equation<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-233 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-75.png\" alt=\"\" width=\"592\" height=\"39\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-75.png 592w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-75-300x20.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-75-65x4.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-75-225x15.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-75-350x23.png 350w\" sizes=\"auto, (max-width: 592px) 100vw, 592px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-234\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-76.png\" alt=\"\" width=\"811\" height=\"118\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-76.png 849w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-76-300x43.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-76-768x111.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-76-65x9.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-76-225x33.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-76-350x51.png 350w\" sizes=\"auto, (max-width: 811px) 100vw, 811px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-235 size-full alignnone\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-77.png\" alt=\"\" width=\"703\" height=\"79\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-77.png 703w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-77-300x34.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-77-65x7.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-77-225x25.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-77-350x39.png 350w\" sizes=\"auto, (max-width: 703px) 100vw, 703px\" \/><\/p>\n<p><span style=\"text-align: initial;font-size: 1em\">Every physical quantity cannot be categorized as belonging to the set of scalars and vectors. There are others that transform in a more complicated way under rotations. Any set of nine physical quantities which transforms in the following way under rotations are said to form a <\/span><em style=\"text-align: initial;font-size: 1em\">tensor of rank two:<\/em><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-236 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-78.png\" alt=\"\" width=\"525\" height=\"34\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-78.png 525w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-78-300x19.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-78-65x4.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-78-225x15.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-78-350x23.png 350w\" sizes=\"auto, (max-width: 525px) 100vw, 525px\" \/><\/p>\n<\/div>\n<div>\n<p><span style=\"text-align: initial;font-size: 1em\">\u00a0 \u00a0 Moment of inertia, stress and strain, and Maxwell\u2019s stress tensor are all examples of tensors of rank two. Vectors can be regarded as <\/span><em style=\"text-align: initial;font-size: 1em\">tensors of rank one<\/em><span style=\"text-align: initial;font-size: 1em\"> and scalars as <\/span><em style=\"text-align: initial;font-size: 1em\">tensors of rank zero<\/em><span style=\"text-align: initial;font-size: 1em\">.<\/span><\/p>\n<\/div>\n<p><span style=\"text-align: initial;font-size: 1em\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-237 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-79.png\" alt=\"\" width=\"853\" height=\"104\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-79.png 853w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-79-300x37.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-79-768x94.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-79-65x8.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-79-225x27.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-79-350x43.png 350w\" sizes=\"auto, (max-width: 853px) 100vw, 853px\" \/><\/span><\/p>\n<div>\n<p style=\"padding-left: 30px\"><strong>4.1 Pseudo Tensors<\/strong><\/p>\n<\/div>\n<div>\n<p>Certain further properties of the transformation coefficients are interesting. Let us take the determinant of both sides of equation (16)<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-238 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-80.png\" alt=\"\" width=\"589\" height=\"39\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-80.png 589w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-80-300x20.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-80-65x4.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-80-225x15.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-80-350x23.png 350w\" sizes=\"auto, (max-width: 589px) 100vw, 589px\" \/><\/p>\n<p>Now for the identity transformation, det(<em>a<\/em>)=1. Since rotation is a continuous transformation, under any rotation det(<em>a<\/em>) will change continuously. Since det(<em>a<\/em>) is allowed only two values, +1 or -1, <em>det(a)=1 under any<\/em> <em>continuous rotation<\/em>. On the other hand for a reflection in a plane, say the<em> z=0 <\/em>plane, we have<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-239 aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-81.png\" alt=\"\" width=\"189\" height=\"33\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-81.png 189w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-81-65x11.png 65w\" sizes=\"auto, (max-width: 189px) 100vw, 189px\" \/><\/p>\n<\/div>\n<div>\n<p>This is represented by the transformation matrix<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-240 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-82.png\" alt=\"\" width=\"631\" height=\"110\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-82.png 631w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-82-300x52.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-82-65x11.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-82-225x39.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-82-350x61.png 350w\" sizes=\"auto, (max-width: 631px) 100vw, 631px\" \/><\/p>\n<p><span style=\"text-align: initial;font-size: 1em\">The same is true of inversion in three dimensions Based on this we have the following results<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-241\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-83.png\" alt=\"\" width=\"811\" height=\"454\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-83.png 840w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-83-300x168.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-83-768x430.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-83-65x36.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-83-225x126.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-83-350x196.png 350w\" sizes=\"auto, (max-width: 811px) 100vw, 811px\" \/><\/p>\n<\/div>\n<div>\n<p style=\"padding-left: 60px\"><span style=\"text-decoration: underline\"><strong>5.\u00a0 Playing with indices<\/strong><\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-242 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-84.png\" alt=\"\" width=\"499\" height=\"33\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-84.png 499w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-84-300x20.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-84-65x4.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-84-225x15.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-84-350x23.png 350w\" sizes=\"auto, (max-width: 499px) 100vw, 499px\" \/><\/p>\n<\/div>\n<div><\/div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-243 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-85.png\" alt=\"\" width=\"867\" height=\"532\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-85.png 867w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-85-300x184.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-85-768x471.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-85-65x40.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-85-225x138.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-85-350x215.png 350w\" sizes=\"auto, (max-width: 867px) 100vw, 867px\" \/><\/p>\n<div>\n<p style=\"padding-left: 30px\"><strong>5.1 The Kronecker delta and permutation symbol<\/strong><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-244\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-86.png\" alt=\"\" width=\"805\" height=\"363\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-86.png 858w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-86-300x135.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-86-768x346.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-86-65x29.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-86-225x101.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-86-350x158.png 350w\" sizes=\"auto, (max-width: 805px) 100vw, 805px\" \/><\/p>\n<\/div>\n<div>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-245 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-87.png\" alt=\"\" width=\"859\" height=\"444\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-87.png 859w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-87-300x155.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-87-768x397.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-87-65x34.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-87-225x116.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-87-350x181.png 350w\" sizes=\"auto, (max-width: 859px) 100vw, 859px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-246\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-88.png\" alt=\"\" width=\"811\" height=\"173\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-88.png 854w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-88-300x64.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-88-768x164.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-88-65x14.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-88-225x48.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-88-350x75.png 350w\" sizes=\"auto, (max-width: 811px) 100vw, 811px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-248 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-90.png\" alt=\"\" width=\"764\" height=\"342\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-90.png 764w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-90-300x134.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-90-65x29.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-90-225x101.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-90-350x157.png 350w\" sizes=\"auto, (max-width: 764px) 100vw, 764px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-249\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-91.png\" alt=\"\" width=\"804\" height=\"342\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-91.png 833w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-91-300x127.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-91-768x326.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-91-65x28.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-91-225x96.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-91-350x149.png 350w\" sizes=\"auto, (max-width: 804px) 100vw, 804px\" \/><\/p>\n<\/div>\n<div>\n<p style=\"padding-left: 60px\"><span style=\"text-decoration: underline\"><strong>6. Vector Identities<\/strong><\/span><\/p>\n<p style=\"text-align: justify\">Many of the vector relations can be proved more conveniently by using the \u201ctensor notation\u201d. Let us, as an example, consider<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-250 size-full aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-92.png\" alt=\"\" width=\"585\" height=\"52\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-92.png 585w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-92-300x27.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-92-65x6.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-92-225x20.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-92-350x31.png 350w\" sizes=\"auto, (max-width: 585px) 100vw, 585px\" \/><\/p>\n<\/div>\n<div>\n<p>To use the \u201ctensor methods\u201d to prove this relation, let us find the <em>i<\/em>th component of left hand side:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-251\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-93.png\" alt=\"\" width=\"800\" height=\"195\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-93.png 862w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-93-300x73.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-93-768x187.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-93-65x16.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-93-225x55.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-93-350x85.png 350w\" sizes=\"auto, (max-width: 800px) 100vw, 800px\" \/><\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p><strong>The differential operator as a tensor<\/strong><\/p>\n<p>The differential operators can obviously also be written in the tensor notation. Thus we have<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-252\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-94.png\" alt=\"\" width=\"279\" height=\"219\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-94.png 279w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-94-65x51.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-94-225x177.png 225w\" sizes=\"auto, (max-width: 279px) 100vw, 279px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-253\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-95.png\" alt=\"\" width=\"807\" height=\"264\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-95.png 856w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-95-300x98.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-95-768x251.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-95-65x21.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-95-225x74.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-95-350x114.png 350w\" sizes=\"auto, (max-width: 807px) 100vw, 807px\" \/><\/p>\n<\/div>\n<div>\n<p style=\"padding-left: 30px\"><span style=\"text-decoration: underline\"><strong>7. The Kronecker delta and permutation symbol as tensors<\/strong><\/span><\/p>\n<p style=\"text-align: justify\">We have so far defined Kronecker delta and permutation symbol as simply that, as objects having specific components. But these are indeed tensors in the sense that they have the required transformation properties under rotations. On using equations (13) and (22) we have<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-254\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-96.png\" alt=\"\" width=\"812\" height=\"363\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-96.png 866w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-96-300x134.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-96-768x343.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-96-65x29.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-96-225x101.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-96-350x156.png 350w\" sizes=\"auto, (max-width: 812px) 100vw, 812px\" \/><\/p>\n<p>&nbsp;<\/p>\n<p><strong>7.1 Isotropic tensors<\/strong><\/p>\n<p>An isotropic tensor is one that has the same components in all rotated frames of reference, i.e.,<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-255 aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-97.png\" alt=\"\" width=\"135\" height=\"42\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-97.png 135w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-97-65x20.png 65w\" sizes=\"auto, (max-width: 135px) 100vw, 135px\" \/><\/p>\n<p>We can classify isotropic tensors as follows:<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-256 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-98.png\" alt=\"\" width=\"770\" height=\"54\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-98.png 770w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-98-300x21.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-98-768x54.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-98-65x5.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-98-225x16.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-98-350x25.png 350w\" sizes=\"auto, (max-width: 770px) 100vw, 770px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-257 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-99.png\" alt=\"\" width=\"579\" height=\"126\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-99.png 579w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-99-300x65.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-99-65x14.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-99-225x49.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-99-350x76.png 350w\" sizes=\"auto, (max-width: 579px) 100vw, 579px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-259\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-101.png\" alt=\"\" width=\"812\" height=\"451\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-101.png 858w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-101-300x166.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-101-768x426.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-101-65x36.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-101-225x125.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-101-350x194.png 350w\" sizes=\"auto, (max-width: 812px) 100vw, 812px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-260\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-102.png\" alt=\"\" width=\"802\" height=\"137\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-102.png 839w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-102-300x51.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-102-768x131.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-102-65x11.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-102-225x38.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-102-350x60.png 350w\" sizes=\"auto, (max-width: 802px) 100vw, 802px\" \/><\/p>\n<\/div>\n<div>\n<p style=\"padding-left: 30px\"><strong>7.2 Physical significance of isotropic tensor of rank two<\/strong><\/p>\n<p>An isotropic tensor behaves much like a scalar. Consider for example the conductivity tensor. In an anisotropic medium the relation between the electric field and the current density takes the form<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-261 aligncenter\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-103.png\" alt=\"\" width=\"98\" height=\"31\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-103.png 98w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-103-65x21.png 65w\" sizes=\"auto, (max-width: 98px) 100vw, 98px\" \/><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-262\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-104.png\" alt=\"\" width=\"809\" height=\"100\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-104.png 871w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-104-300x37.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-104-768x95.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-104-65x8.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-104-225x28.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-104-350x43.png 350w\" sizes=\"auto, (max-width: 809px) 100vw, 809px\" \/><\/p>\n<\/div>\n<div>\n<p style=\"padding-left: 30px\"><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-263 size-full\" src=\"http:\/\/msp01.epgpbooks.inflibnet.ac.in\/wp-content\/uploads\/sites\/95\/2018\/11\/2-105.png\" alt=\"\" width=\"853\" height=\"244\" srcset=\"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-105.png 853w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-105-300x86.png 300w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-105-768x220.png 768w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-105-65x19.png 65w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-105-225x64.png 225w, https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-content\/uploads\/sites\/95\/2018\/11\/2-105-350x100.png 350w\" sizes=\"auto, (max-width: 853px) 100vw, 853px\" \/><\/p>\n<\/div>\n<p style=\"padding-left: 30px\"><strong>SUMMARY<\/strong><\/p>\n<ul>\n<li>In this module we develop a new perspective for the idea of vectors which are related to properties of physical quantities under rotation.<\/li>\n<li>We introduce the so called tensor notation which is a big help in this study of rotational properties.<\/li>\n<li>Next we introduce and explain with examples the Einstein summation convention which simplifies the formalism even further.<\/li>\n<li>We then define vectors from this new perspective of properties of physical quantities under rotations in the three dimensional physical space. We then generalize the idea to tensors of second and higher order ranks and explain how scalars and vectors are tensors of rank zero and one respectively.<\/li>\n<li>Next we further classify physical quantities on the basis of their behaviour under inversion of the coordinate axes and introduce true and pseudo tensors.<\/li>\n<li>In this tensor (or index) notation the indices play a very important role and we demonstrate how playing around with indices leads to many significant results.<\/li>\n<li>Next we formally introduce two very special tensors, the Kronecker delta and the permutation tensor and discuss their usefulness and properties.<\/li>\n<li>Next we write down certain vector identities and demonstrate how the tensor methods greatly simplify the derivation of such identities.<\/li>\n<li>Next we prove that Kronecker delta and the permutation tensor that were introduced are indeed tensors of rank two and three respectively.<\/li>\n<li>Finally we briefly discuss the idea of isotropic tensors and describe isotropic tensors of rank up to four.<\/li>\n<\/ul>\n","protected":false},"author":3,"menu_order":4,"template":"","meta":{"_acf_changed":false,"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-215","chapter","type-chapter","status-publish","hentry"],"part":3,"_links":{"self":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/pressbooks\/v2\/chapters\/215","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/wp\/v2\/users\/3"}],"version-history":[{"count":4,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/pressbooks\/v2\/chapters\/215\/revisions"}],"predecessor-version":[{"id":265,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/pressbooks\/v2\/chapters\/215\/revisions\/265"}],"part":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/pressbooks\/v2\/parts\/3"}],"metadata":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/pressbooks\/v2\/chapters\/215\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/wp\/v2\/media?parent=215"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/pressbooks\/v2\/chapter-type?post=215"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/wp\/v2\/contributor?post=215"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/ebooks.inflibnet.ac.in\/msp01\/wp-json\/wp\/v2\/license?post=215"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}