Second Law of Thermodynamics What is the second law of thermodynamics

The second law of thermodynamics simply states that whenever work is done, or when thermal process is performed a portion of the energy is transformed into unusable energy.  More complex a system a is the more processes it has, the more energy is transformed into unusable energy.

Important Equations  Qh = Input heat

Qc = Output heat

Th = Temperature of the gas when heat is added

Tc = Temperature of the gas when heat is removed

Heat Pathways

Thermal radiation is electromagnetic radiation emitted from a material which is due to the heat of the material, the characteristics of which depend on its temperature. An example of thermal radiation is the infrared radiation emitted by a common household radiator or electric heater. A person near a raging bonfire will feel the radiated heat of the fire, even if the surrounding air is very cold

Definition provided by Wikipedia

Conduction

Heat conduction (as opposed to electrical conduction) is the flow of internal energy from a region of higher temperature to one of lower temperature by the interaction of the adjacent particles (atoms, molecules, ions, electrons, etc.) in the intervening space. Simply put, conduction occurs when two objects are in direct contact.

Definition provided by Physics Hypertextbook

Convection

Convection is the flow of heat through a bulk, macroscopic movement of matter from a hot region to a cool region, as opposed to the microscopic transfer of heat between atoms involved with conduction. Suppose we consider heating up a local region of air. As this air heats, the molecules spread out, causing this region to become less dense than the surrounding, unheated air. For reasons discussed in the previous section, being less dense than the surrounding cooler air, the hot air will subsequently rise due to buoyant forces - this movement of hot air into a cooler region is then said to transfer heat by convection.

Definition provided by University of Winnipeg

The easiest way to look at convection is a method of heat transfer that requires a medium.  This medium is called a fluid, a group of atoms and molecules that can move free about (gases and liquids are both fluids).

Efficiency

Equation for Efficiency