Detail explanation of laws of thermodynamics?

Thermodynamics is the branch of physics which is mainly concerned with the transformation of heat into mechanical work. It involves the study of the interaction of one body on another, the interaction being described in terms of the quantities of heat and work. Thus thermodynamics may be said to be an exact mathematical since that describes the inter-relationship between heat and mechanical energy. With the passage of time ,however , the scope of thermodynamics has increased and nowadays it covers all the branches of physics as well as chemistry whenever we have to deal with heat and it's relationship to energy in any of its diverse forms electrical , mechanical, chemical and magnetic etc. Thermodynamics is based in two laws of nature which govern the conservation between heat and mechanical work while the second law depicts the manner in which these energy changes take place. Thermodynamics takes no account of the atomic constitution of matter. Here we only deal with macroscopic properties and do not go into the detailed structure. The two laws of thermodynamics are as follows

1) First law: The first law is one which expresses the equivalence between mechanical work and heat energy. It states that, " When mechanical work is spent in producing heat ,a definite quantity of heat is produced for each unit of work spent ; and conversely ,when heat is employed to do work, the same definite quantity of heat disappears for every unit of work obtained ". Thus if W is the amount of work, then amount of heat Q that can be produced by it is given by

W = JQ , where J=4.2x10^7ergs/cal is a universal constant called the mechanical equivalent of heat.

2) Second law of thermodynamics : It states that," In all transformations, the energy due to heat units supplied must be balanced by the external work done plus the increase in internal energy". If dUk and dUp are the internal kinetic energy and internal potential energy and dW be external work done then we have , dQ = dUk + dUp + dW. Since dUk + dUp = dU, then we can write dQ = dU + dW. Here dQ,dU and dW are measured in the same units i.e., all the three either in Joules or in calories. If the heat is taken by the system then dQ is positive and if it is given by system dQ is negative. Also if work is done by system then dW is positive and if work is done by external agency on system then dW is negative.