Phy301A: Energy

Basic InformationThis course has some other numbers: Phy301 (1 student), SE308(0 students). Phy301A (150+ students)

Details of Lectures: Total number of Lectures: about 40

Syllabus OutlineSyllabus Outline: Basic concept of energy, energy in the biosphere and human history, fossil fuels, renewable energy, the Indian situation.

Special TopicsSpecial Topics: Global warming and Ice ages, biofuels and their dangers, nuclear energy and its difficulties, fusion and cold fusion, fossil fuels and our civilization, peak oil, carbon sequestration, the problems of wind and solar energy, ...

28 July 2015 Phy301A: Energy 2

Lecture plan:

Basic Concepts (2-3 lectures)Energy in the Biosphere (7-8)Energy in Human History (7-8)Present: Fossil Fuels (10-12)Future: Renewable Energy (7-9)The Indian Situation (3-4)

Grading scheme:

Two quizzes (10+10 marks), Mid-Sem (40 marks), End-Sem (60 marks), Projects (20 marks), Attendance (20 marks)

Marks for attendance = 20*x*H(x)where x = (Fractional Attendance 0.6) and H(x) is the Heaviside step function. Attendance will be taken on a few days randomly.

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Books/References: Energy: a beginners guide by Vaclav Smil, Oneworld publicaions, Oxford, England (2006) (Available in the market for about Rs.200: flipkart, infibeam, amazon, )Energy in Nature and Society: General Energetics of Complex Systems by Vaclav Smil, The MIT Press, Cambridge, Massachusetts (2008)WikipediaEncyclopedia of Energy, Elsevier (2004) (Available online through sciencedirect and in IITK library) India Energy Book 2012, World Energy Council. (Freely downloadable from the internet): Statistical Review of World Energy 2015 (www.bp.com)

Course Website:Will be set up on Piazza.com. Will be used for sharing course material, for discussions and for projects.

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Lecture 1: Basic ConceptsAristotle (384322 b.c.e.) created the term (energeia) to mean actuality, identified with movement. According to Aristotle, every objects existence is maintained by energeia related to the objects function. The word thus came to signify motion, action, work and change.

No progress for the next 2000 years. Newton did not talk about it. Then Thomas Young (17731829) of double slit interference expt & Young's modulus fame defined energy as mv2. He was obviously talking about kinetic energy. At that time other forms of energy were not known!

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The concept of energy reached a state of clarity in 19th century with the maturing of Newtonian mechanics and the engineering experiments conducted by James Watt (17361819; improvement of steam engine) et. al. The SI unit of power isnamed after him.

In early 19th Century Sadi Carnot (17961832) elucidated principles of converting heat energy to kinetic energy.

Soon after Justus von Liebig (18031873), one of the founders of biochemistry and modern agriculture, offered a correct interpretation of human and animal metabolism ascribing the generation of carbon dioxide and water to the oxidation of food.

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Julius Robert Mayer (18141878), a physician and physicist, arrived at the conclusion that the various forms of energy must be convertible from one form to another hinting at the law of conservation of energy (first law of thermodynamics).

The English physicist James Prescott Joule (18181889) arrived at the equivalence of heat and mechanical energy by his careful experiments (4.2J/cal). The SI unit of energy is named in his honor.

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In 1850 the German theoretical physicist Rudolf Clausius (18221888) proved that the maximum performance obtainable from an engine depends only on the temperatures of the heat reservoirs, and that there can never be a heat flow from a colder to a hotter body.

In 1865 Clausius coined the term entropy as a measure of the degree of disorder in a closed system. Clausius formulated the law: entropy of the universe tends to a maximum (second law of thermodynamics).

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Heat energy was found to be something special. Other forms of energy can be converted to heat completely. Conversion of heat into other forms is never complete. Only a portion of the input heat can be converted to another form. Example: An internal combustion engine.

The second law of thermodynamics also pointed towards the heat death of the Universe when temperatures everywhere will become equal. There will be complete disorder as entropy would reach its maximum value, and there will be perfect thermodynamic equilibrium.

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In living organisms second law of thermodynamics gets apparently violated all the time. Living organisms seem to be creating order out of disorder. How?

The apparent violation is due to living organisms being open systems. They are always collecting energy from and losing energy to the surroundings. Second law applies to closed systems only. Here we have non-equilibrium thermodynamics in operation.

Message: Energy flow can create order out of chaos! And this applies to living beings, biosphere, civilizations and other man made objects and structures.

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At the beginning of 20th century Albert Einstein showed that E=mc2 indicating that matter and energy are equivalent. Matter can be converted to energy and vice versa. This was an unexpected extension of the law of conservation of energy (first law of thermodynamics).Just six tonnes of matter contain energy that is equal to the worlds annual consumption of commercial energy (520 EJ for the year 2008). But it is not easy to release the energy locked up as matter. Nuclear fission achieves the maximum conversion of matter to energy for commercial energy production. 235U fission coverts 0.1% of the material to energy.

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Energy comes in many forms: heat (thermal energy), light (electromagnetic radiation), motion (mechanical energy), electricity, chemical energy of food and fuel. These forms of energy convert among themselves over huge time and length scales.

Example: lightning converts electrical energy light, sound, heat, chemical energy over a timescale of a fraction of a second.A thermal power station converts chemical energy in coal thermal energy electrical energy over a period of decades.

Energy conversions are intimately connected with life. For example photosynthesis: electromagnetic energy from Sun chemical energy of bacteria and plants. Cooking and heating is done by converting chemical energy in biomass (wood, charcoal, straw) or fossil fuels (coals, oils, gases) to thermal energy.

Energy and its transformations

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Some Energy Transitions

From To

Electromagnetic

Chemical Thermal Mechanical Electrical Nuclear

Electro-magnetic

Chemilum-inescence

Thermal radiation

Accelerating charge

Electrolumine-scence

Gamma rays

Chemical Photosyn-thesis

ChemicalReaction

Dissociat-ion

ElectrolysisCharging a battery

Ionization

Thermal Absorption Combust-ion

Heat exchange

Friction Electrical heating

Fission

Mechanical Muscles Thermal expansion

Gears Motor Radioact-ivity

Electrical Solar cells BatteriesFuel cells

Thermoelectricity

Generator Nuclear batteries

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Conversion Efficiency: some numbersEfficiency = Desirable output / input

Photosynthesis: Converts solar energy to biomass. is at best 5% for the most productive crops. Global annual average is only 0.3%! Resistive heating: electricity heat; can go up to 100%Electrical motors: electricity kinetic energy; can be up to 95%Turbines in thermal stations: kinetic energy electricity; best 99%. Overall of a steam turbine plant can reach up to 47%. Internal combustion engine: chemical energy kinetic energy; best : petrol car engine: 25-30%, diesel engine: 40% Photovoltaic converter: sun light electricity varies from 6% to 44%

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Our favorite form of energy: Electricity Not a primary form but a preferred form. Extremely easy to

use and control. Alternating current is standard for mains supplies. Direct

current from batteries for small devices. In India mains supply is 220 V, 50 Hz. In north America it is

120V, 60Hz. Rest of the world 220-230V, 50Hz mostly. Advantage of ac supply: Easy to change voltage using

transformers. Long distance transmission at high voltages such as 110 kV etc. This helps to minimize transmission losses.

Aluminum wires are usually used for long distance electricity transmission because they have high electrical conductivity and are also cheap compared to Copper.

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Electricity - contd Metallic conductors obey Ohm's law (R=V/I). Power dissipated

in a conducting wire VI = I2R Fatal shocks from electricity depends on the current that

passes through the body. 100 mA can be a fatal current. Household appliances typically use from a few watts of power

to a few kilowatts. A rechargeable pencil cell can store up to 10 kJ of energy. Indian electricity generation capability is 260GW (as of May

2013). India generated 855TWh = 3.1EJ in 2011-12. Nonrenewable sources (coal, natural gas, lignite, nuclear)

contribute 87.5% of the above. Rest 12.5% from renewables (hydroelectricity, wind & solar)

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Links to Videos Shown in Class

Mechanical equivalent of heat: https://www.youtube.com/watch?v=MBrTDKc9YZ0

Steam Engine Made of Glass: https://www.youtube.com/watch?v=73txXT21aZU

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