The knowledge of the physical world later expanded to include such areas as heat, sound, electricity and magnetism, followed by the idea of conservation of energy. Energy exists in many forms, such as heat, light, chemical energy, and electrical energy. Thermodynamics is the study of energy and the laws of thermodynamics govern the energy transformations. The First Law of Thermodynamics (conservation) states that energy is always conserved, it cannot be created or destroyed. In essence, energy can be converted from one form into another. The contribution of Rudolf Clausius is immense through his famous second law of thermodynamics which states that in any closed system, the entropy of the system will either remain constant or increase. The most efficient heat engine cycle is the Carnot cycle, consisting of two isothermal processes and two adiabatic processes and the second law of thermodynamics sets the limiting value on the efficiency of Carnot cycle.
Michael Faraday discovered the connections between the phenomena of electricity and magnetism by observing that the flow of electric charge through a wire caused magnetic effects, and a changing magnetic field could produce a current in a closed loop of wire. He summarized his historic discovery in a single statement: "Whenever a magnetic force increases or decreases, it produces electricity; the faster it increases or decreases, the more electricity it produces". Amount of electricity produced by magnetism was equal to the rate of increase or decrease of the magnetic force. It was said that Faraday has seen the world through the eyes of poet by seeing simplicity while there is complexity. And then, toward the end of the century, the great physicist James Clerk Maxwell showed how, by uniting the equations that described electric and magnetic fields, he could account for the transmission of light through space at the amazing speed of about 3 × 108 meters per second, a value that was already known from experiment. The net result was a tremendous unification of physics. The Faraday's law is very significant as it changed the world leading to development of electric motors, generators and everything that works on electricity.