In applying Kirchhoff's laws to electrical networks, the question of assuming proper directionof current usually arises. The direction of current flow may be assumed either clockwise oranticlockwise. If the assumed direction of current is not the actual direction, then on solving thequesiton, this current will be found to have a minus sign. If the answer is positive, then assumeddirection is the same as actual directionElectric circuit analysis with the help of Kirchhoff's laws usually involves solution of two orthree simultaneous equations. These equations can be solved by a systematic elimination of thevaria~les but the procedure is often lengthy and laborious and hence more liable to error. Determinantsand Cramer's rule provide a simple and straight method for solving network equations throughmanipulation of their coefficients. Of course, if the number of simultaneous equaitons happens to bevery large, use of a digital computer can make the task easy.It is defined as the ratio of the heat actualy utilized to the total heatJ>roducedelectrically. Considerthe case of the electric kettle used for boiling water. Out of the total heat produced (i) somegoes to heat the apparatus itself i.e. kettle (ii) some is lost by radiation and convection ect. and(iii) the rest is utilized for heating the water. Out of these, the heat utilized for useful purpose is thatin (iii). Hence, thermal efficiency of this electric apparatus is the ratio of the heat utilized for heatingthe waterto the total heatproduced