Abstract
This paper discusses and answers the questions related to the laws of thermodynamics, differences between potential energy and kinetic energy, and differences between overall efficiency and efficiency of a light bulb. Current knowledge regarding thermodynamics has been applied to answer these questions with help of online resources.
1) How are the laws of thermodynamics an important consideration when trying to make the most efficient mechanical machines to do work (such as create light)?
A) The Zeroth law of thermodynamics is the fundamental law of physics, which suggests that if two bodies are in thermal equilibrium, and one of these bodies is in thermal equilibrium with a third body, all the three bodies are then in thermal equilibrium with each other (Fermi, 1956). Hence, it describes how energy may flow through objects connected with each other until the level of energy concentration becomes equal in all of the objects (Fermi, 1956).
First thermodynamic law states that energy can neither be created nor be destroyed; it can only be converted from one form to the other (Pianka, 2013). This gives a clear idea that energy can be converted into different forms and that all forms of energy are interchangeable.
Second law of thermodynamics states that an isolated system spontaneously evolves towards thermodynamic equilibrium (Pianka, 2013). In other words, when components of a system are out of equilibrium are allowed to remain undisturbed, they exchange thermal energy and settle down to produce a form of dynamic thermal equilibrium.
Third law of thermodynamics states that entropy of an isolated system nearly achieves a value that is constant as the temperature drops to zero, which means that entropy of the isolated system at “absolute zero” (0 Kelvin or -273.15 oC) is zero and is determinable only by total number of ground states (PhysicsClassroom.com, 2013).
The laws of thermodynamics are applicable to any mechanism that performs any kind of energy conversion to work, it will require some form of energy, so that it may be able to utilize it and generate a desired form of energy (Fermi, 1956). For example, in case of generation of light energy, some form of energy, heat, chemical or electrical must flow into a mechanism which may become luminescent and produce light energy through the excitement of molecular as well as sub atomic particles (Fermi, 1956).
2) Contrast potential and kinetic energy. Give examples of each in the power industry.
A) Potential energy is a form of mechanical energy which comes into play either due to the gravitational pull generated by the height at which it is placed can, or the opposition that a body may store in it when an external force distorts its dimensions (McCall, 2010). It may be represented by the mathematical relation:
Potential Energy = mass of object x acceleration due to gravity x height of object
All bodies at rest must possess potential energy if their state of rest is to be converted into motion (McCall, 2010). In Power Industry potential energy finds great use, as in the classic example of water reservoirs in a hydroelectric power plant, where water from a plentiful source is collected in a space where it can gain enough height to create potential energy enough to turn power turbines when this water is allowed to fall on it (McCall, 2010).
Kinetic energy is the form of mechanical energy that a moving body possesses (PhysicsClassroom.com, 2013). It is simply present in a body due to its state of motion. In an equation it may be represented as:
Kinetic Energy – 0.5 mass x velocity
All of the potential energy stored in a body by virtue of its height or physical stress is converted into kinetic energy as the body starts moving from rest (PhysicsClassroom.com, 2013). In our example of a hydroelectric power plant, the reservoir that has been stored at a height is let loose in a controlled manner and allowed to fall on to sets of turbines that then rotate to generate power (PhysicsClassroom.com, 2013). It must be noted that all this motion indicates kinetic energy which was converted from the stored potential energy in the water reservoir. Hence, potential energy and kinetic energy may be produced due to the state of rest and state of motion of a body, but they are interchangeable completely. However, there may be losses of energy in practical life during the conversion of energy in the form of heat energy (McCall, 2010).
3) Contrast overall efficiency and efficiency of a light bulb.
A. Overall efficiency is a ratio between the work done by the system or mechanism to the amount of energy that has been put into the system (Krueger, 2009). It is represented by Ƞ and mathematically represented as:
η= Work Done or Power GeneratedRate of Input Energy
Overall efficiency of any device cannot exceed one because the first law of thermodynamics limits it as so because energy can only be changed in forms, and in real practice the second law of thermodynamics renders it less than one as there will be loss of energy in the form of heat energy (Krueger, 2009).
The efficiency of a normal 60 to 100 watt 120 volt bulb is approximately 0.1, as an average light bulb converts most of the electrical energy supplied to it in the form of heat energy and only 10% of the electrical energy gets converted into incandescent light energy. It may be added here that this means that common light bulbs have less energy efficiency in comparison to LED and CFL bulbs (Fleischhauer, Kleinhubbert and Neubacher, 2010).
References
Fermi, Enrico (1956). Thermodynamics, Courier Dover Publications. p. ix. ISBN 0-486-60361-X. OCLC 230763036 54033021 http://books.google.com/?id=VEZ1ljsT3IwC&printsec=frontcover; retrieved - 29 July 2013
Fleischhauer, Jan; Kleinhubbert, Guido; Neubacher, Alexander (17 March 2010) “Is Environmentalism Really Working: Germany's Eco-Trap". Der Spiegel; http://www.spiegel.de/international/germany/germany-s-eco-trap-is-environmentalism-really-working-a-751469.html; retrieved - 29 July 2013.
Krueger, Paul S. (2009) Making a Move: A Brief Introduction to Mechanical and Biological Propulsion; National Science Foundation; http://lyle.smu.edu/propulsion/Pages/efficiency.htm; Accessed - 29 July, 2013
McCall, Robert P. (2010). "Energy, Work and Metabolism". Physics of the Human Body. JHU Press. P.74; ISBN 978-0-8018-9455-8. http://books.google.com/books?id=LSyC41h6CG8C&pg=PA74; retrieved - 29 July 2013
PhysicsClassroom.com (2013). Basic Terminology and Concepts. The Physics Classroom http://www.physicsclassroom.com/class/energy/u5l1c.cfm; retrieved - 29 July 2013
Pianka, Eric R. (2013) Laws of Thermodynamics; School of Biological Sciences http://www.zo.utexas.edu/courses/Thoc/Thermodynamics.html; retrieved - 29 July 2013.
