* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Thermodynamics is the s
Quantum logic wikipedia , lookup
Electron scattering wikipedia , lookup
Compact Muon Solenoid wikipedia , lookup
Interpretations of quantum mechanics wikipedia , lookup
Quantum chaos wikipedia , lookup
Scalar field theory wikipedia , lookup
Relativistic quantum mechanics wikipedia , lookup
Quantum vacuum thruster wikipedia , lookup
Relational approach to quantum physics wikipedia , lookup
Nuclear structure wikipedia , lookup
Standard Model wikipedia , lookup
Theory of everything wikipedia , lookup
History of quantum field theory wikipedia , lookup
Renormalization wikipedia , lookup
Canonical quantization wikipedia , lookup
Atomic nucleus wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
Eigenstate thermalization hypothesis wikipedia , lookup
Introduction to quantum mechanics wikipedia , lookup
Elementary particle wikipedia , lookup
Thermodynamics This lecture note includes information derived from various internet sources. What is it? Thermodynamics is the study of heat and its effects on matter. Thermodynamics follows four basic laws. Give me an example! It is important to understand thermodynamics because heat often changes the chemical and physical properties of things. For example, the air inside the same automobile tire on a cold day takes up less space than that same air in that same tire on a hot day. Matter What is it? Matter is the substance that everything is made of. Matter can exist in a gas, liquid, or solid state. Matter can be a pure element or any type of compound. All Matter has three basic characteristics: First, matter has volume (takes up space). Second, matter has mass (or can be weighed). And third, matter has inertia. Give me an example! Water is matter which is all around us in many forms. We drink it as a liquid. We use it to cool things in its solid state (ice). And we use it for heat when it's a gas (steam). It's all the same matter - just in different states. Inertia What is it? In physics, inertia is the force of nature that makes matter tend to maintain or stay in its current state of motion. Inertia is the resistance of objects to any change in their speed. Every object has inertia, and the amount of inertia an object has is directly related to the amount of mass it has; the more mass, the more inertia, and therefore the more resistance to change in speed. In chemistry, inert substances are those which will not react with others. There is a group of elements in the periodic_table_of_the_elements called the "Noble Gasses" which are chemically inert. You can find them on the right side of the periodic table in the very last column, under helium (He). Give me an example! Have you ever pulled a toy wagon? Did you notice that the more things you put into the wagon - the more mass it contained - the harder it was to pull? That's because the more mass the wagon contained, the more inertia acted upon it. First Law of Thermodynamics What is it? The First Law of Thermodynamics states that the amount of heat energy contained within a closed system is always constant. This is the basis of the principle of conservation_of_energy. Give me an example! When a battery powered light is switched on and heat is produced, that heat energy actually already existed inside the system as chemical energy inside the battery. So no energy is either gained or lost as a result of switching on the light. Conservation of Energy What is it? Conservation of energy is a physical_law which states that energy can be converted to a different form, but it is never lost all together. Give me an example! When the internal_combustion_engine in an automobile burns gasoline, it produces heat energy. The engine then uses this heat to drive pistons and turn a crankshaft, converting the heat to mechanical energy. The heat energy is not lost - merely changed to another kind of energy. Zeroth Law of Thermodynamics What is it? The Zeroth Law of Thermodynamics states that if two systems both achieve thermodynamic_equilibrium with a third system, then the two systems will also be in equilibrium with each other, too. Give me an example! If you set a pan of boiling water and a tray of ice cubes out in the same room for several hours, the temperature of the boiling water will decrease to the temperature of the room - and the ice will melt and therefore increa Thermodynamic Equilibrium What is it? Thermodynamic equilibrium is when heat ceases to flow between two systems. There is no heat_transfer when thermodynamic equilibrium is reached. Give me an example! If you put a hot cup of coffee or tea in a cold room, heat will flow from the cup and its contents into the room. But if you leave it there for two hours and come back, the cup of coffee or tea will be at the same temperature as the room. The coffee and the room will have achieved a state of thermodynamic equilibrium. Second Law of Thermodynamics What is it? The Second Law of Thermodynamics states that it is impossible to completely convert heat energy into mechanical energy. Another way to put that is to say that the level of entropy (or tendency toward randomness) in a closed system is always either constant or increasing. Give me an example! Have you ever felt the heat from exhaust coming out of the tailpipe of a car? Automobile engines are designed to convert the heat energy resulting from the combustion of gasoline into mechanical energy. However, this process does not function with 100% efficiency - and proof of that is the heat lost along with the exhaust gasses. Entropy What is it? Entropy is the scientific measurement of the change in the randomness or disorder in a chemical system as the result of a reaction. A positive change in entropy means the system is less ordered after the reaction than it was before. Give me an example! Have you ever watched an ice cube melt at room temperature? You were watching entropy in action! As the ice passes from a solid state to a liquid state, the level of entropy (or randomness) of the molecules rises. Third Law of Thermodynamics What is it? The Third Law of Thermodynamics states that the entropy of all crystaline solids approaches zero as their temperature approches absolute_zero. In other words, all substances lose their energy at absolute zero. Give me an example! Have you ever wondered why people keep food in a deep freeze? Lowering the temperature of the food preserves keeps the food from losing energy and decomposing. That way when you want to eat a frozen pizza, you take it out of the freezer, add heat, and you have a hot, mouthwatering meal! Solid What is it? Solid is one of the three states or phases_of_matter. A solid substance does not flow (like a liquid does) and does not take on the shape of the container in which it is being kept (again, like liquids do). If a solid is heated, it will become a liquid once it reaches its melting_point. Give me an example! Have you ever frozen water to make ice? Then you have turned a liquid into a solid. If you melt ice, you are turning a solid into a liquid. Absolute Zero What is it? Absolute zero is the temperature at which no known system can still engage in heat_transfer. Absolute zero is the temperature where all molecular motion ceases. On a Kelvin thermometer, absolute zero is simply "zero." On a Celsius thermometer, absolute zero is at 273 degrees. Absolute zero is the lowest temperature in the world, and has never actually been attained in a laboratory. Give me an example! When you freeze water into ice, the molecules form a solid crystalline structure and move much less than when the water is in its liquid phase. If you continue to lower the temperature of the ice, you will reach a point where all molecular motion comes to a standstill - theoretically, at absolute zero. Temperature What is it? Temperature is a measurement of the amount of heat a substance contains. There are three major temperature scales: Fahrenheit, Celsius, and Kelvin. Give me an example! Have you ever had your temperature taken with a thermometer? The thermometer contains a liquid that is heated by your body and expands inside a tube. Measured markings on the sides of the tube tell how hot you are, which is how the doctor tells whether you have a fever - by taking your temperature. Kelvin What is it? The Kelvin temperature scale is often used in scientific experiments. Zero degrees Kelvin is called absolute zero because it is the temperature where every element in the periodic_table_of_the_elements will freeze. Water will freeze at 273 degrees Kelvin. Water reaches its boiling_point at 373 degrees Kelvin. Give me an example! Converting a Kelvin reading to Celsius is easy - just add 273 to the Kelvin reading. Want to convert a Kelvin temperature to Fahrenheit? First add 273 to the Kelvin reading, and then convert it as if it were a Celsius reading - multiply by 9/5 and add 32. thermodynamics thermodynamics (thûr´mo-dì-nàm´îks), branch of science concerned with the nature of HEAT and its conversion into other forms of energy. Heat is a form of energy associated with the positions and motion of the molecules of a body. The total energy that a body contains as a result of the positions and the motions of its molecules is called its internal energy. The first law of thermodynamics states that in any process the change in a system's internal energy is equal to the heat absorbed from the environment minus the WORK done on the environment. This law is a general form of the law of conservation of energy (see CONSERVATION LAWS). The second law of thermodynamics states that in a system the entropy cannot decrease for any spontaneous process. A consequence of this law is that an engine can deliver work only when heat is transferred from a hot reservoir to a cold reservoir or heat sink. The third law of thermodynamics states that all bodies at absolute zero would have the same entropy; this state is defined as having zero entropy. entropy entropy, quantity specifying the amount of disorder or randomness in a system bearing energy or information. In thermodynamics, entropy indicates the degree to which a given quantity of thermal energy is available for doing useful work-the greater the entropy, the less available the energy. According to the second law of thermodynamics, during any process the change in entropy of a system and its surroundings is either zero or positive; thus the entropy of the universe as a whole tends towards a maximum. In information theory entropy represents the "noise," or random errors, occurring in the transmission of signals or messages. energy energy, in physics, the ability or capacity to do work. Forms of energy include heat, chemical energy, and, according to the theory of relativity, mass; other forms of energy are associated with the transmission of light, sound, and electricity. When a force acts on a body, the work performed (and the energy expended) is the product of the force and the distance over which it is exerted. Potential energy is the capacity for doing work that a body possesses because of its position or condition. For example, a weight lifted to a certain height has potential energy because of its position in earth's gravitational field. Kinetic energy, the energy a body 2 posesses because it is in motion, is equal to ½mv , where m is its mass and v is its velocity. The average kinetic energy of the atoms or molecules of a body is measured by the temperature of the body. Energy (or its equivalent in mass) can be neither created nor destroyed, but it can be changed from one form into another. motion motion, in mechanics, the change in position of one body with respect to another. The study of the motion of bodies is called dynamics. The time rate of linear motion in a given direction by a body is its velocity; this rate is called the speed if the direction is unspecified. If during a time t a body travels over a distance s, then the average speed of that body is s/t. The change in velocity (in magnitude and/or direction) of a body with respect to time is its acceleration. The relationship between force and motion was expressed by Isaac Newton's three laws of motion: A body at rest tends to remain at rest, or a body in motion tends to remain in motion at a constant speed in a straight line, unless acted on by an outside force; The acceleration a of a mass m by a force F is directly proportional to the force and inversely proportional to the mass, or a = F/m; For every action there is an equal and opposite reaction. The third law implies that the total linear momentum (mass m times velocity v) of a system of bodies not acted on by an external force remains constant (see conservation laws). Motion at speeds approaching that of light must be described by Einstein's special theory of relativity, and the motions of extremely small objects (atoms and elementary particles) are described by quantum mechanics. mechanics mechanics (mî-kàn'îks), branch of physics concerned with motion and the forces causing it. The field includes the study of the mechanical properties of matter, such as DENSITY, elasticity (see STRENGTH OF MATERIALS), and VISCOSITY. Mechanics is divided into STATICS, which deals with bodies at rest or in equilibrium, and dynamics, which deals with bodies in motion. Isaac Newton, who derived three laws of motion and the law of universal gravitation, was the founder of modern mechanics. For bodies moving at speeds close to that of light, Newtonian mechanics is superseded by the theory of relativity, and for the study of very small objects, such as elementary particles, quantum mechanics is used. conservation laws conservation laws, in physics, basic laws that maintain that the total value of certain quantities remains unchanged during a physical process. Conserved quantities include mass (or matter), energy, linear momentum, angular momentum, and electric charge; the theory of relativity, however, combines the laws of 2 conservation of mass and of energy into a single law (E=mc ). Additional conservation laws have meaning only on the subatomic level. Special Theory of Relativity relativity (rèl´e-tîv¹î-tê), physical theory, introduced by Albert Einstein, that discards the concept of absolute motion and instead treats only relative motion between two systems or frames of reference. Space and time are no longer viewed as separate, independent entities but rather as forming a four-dimensional continuum called space-time. In 1905 Einstein enunciated the special theory of relativity, in which the hypothesis that the laws of nature are the same in different moving systems also applies to the propagation of light, so that the measured speed of light is constant for all observers regardless of the motion of the observer or of the source of light. From these hypotheses Einstein reformulated the mathematical equations of physics. In most phenomena of ordinary experience the results from the special theory approximate those based on Newtonian dynamics, but the results deviate greatly for phenomena occurring at velocities approaching the speed of light. Among the assertions and consequences of the special theory are the propositions: the maximum velocity attainable in the universe is that of light (c) mass increases with velocity 2 mass and energy are equivalent (E=mc ) objects appear to contract in the direction of motion (Lorentz contraction) the rate of a moving clock seems to decrease as its velocity increases (time dilation) events that appear simultaneous to an observer in one system may not appear simultaneous to an observer in another system. The special theory became the foundation of the study of elementary particles and of quantum mechanics. elementary particles elementary particles, the most basic physical constituents of the universe. Atoms are the basic units of the chemical elements but are themselves composed of smaller particles. The first subatomic particle to be discovered was the electron, identified in 1897 by Joseph John Thomson. The nucleus of ordinary hydrogen was subsequently recognized as a single particle and was named the proton. The third basic particle in an atom, the neutron, was discovered in 1932. Although models of the atom consisting of just these three particles are sufficient to account for all forms of chemical behavior of matter, quantum mechanics predicted the existence of additional elementary particles. Decades of painstaking experiments and theoretical insights have led to a surprisingly simple picture of the world of elementary particles and the laws they obey. According to this physical theory, known as the Standard Model, the most fundamental particles fall into three categories: the leptons, the quarks, and the gauge bosons (force carriers). Leptons include the electrically charged electrons, two unstable particles similar, but heavier than electrons, and neutral particles called neutrinos. Two kinds of quarks, called "up" and "down", make up the protons and neutrons, but heavier, less stable quarks also exist. Gauge bosons give rise to the strong, weak, and electromagnetic forces, which govern the interaction of the quarks and leptons. A more detailed chart summarizes the properties of the particles in the standard model. quantum mechanics or quantum theory quantum mechanics or quantum theory, branch of mathematical physics that deals with the emission and absorption of energy by matter and with the motion of material particles. Because it holds that energy and matter exist in tiny, discrete amounts, quantum mechanics is particularly applicable to elementary particles and the interactions between them. According to the older theories of classical physics, energy is treated solely as a continuous phenomenon (i.e., waves), and matter is assumed to occupy a very specific region of space and to move in a continuous manner. According to the quantum theory, energy is emitted and absorbed in a small packet, called a quantum (pl. quanta), which in some situations behaves as particles of matter do; particles exhibit certain wavelike properties when in motion and are no longer viewed as localized in a given region but as spread out to some degree. The quantum theory thus proposes a dual nature for both waves and particles, with one aspect predominating in some situations and the other predominating in other situations. Quantum mechanics is needed to explain many properties of matter, such as the temperature dependence of the specific heat of solids, as well as when very small quantities of matter or energy are involved, as in the interaction of elementary particles and fields, but the theory of relativity assumes importance in the special situation where very large speeds are involved. Together they form the theoretical basis of modern physics. (The results of classical physics approximate those of quantum mechanics for large scale events and those of relativity when ordinary speeds are involved.) Quantum theory was developed principally over a period of thirty years. The first contribution was the explanation of blackbody radiation in 1900 by Max Planck, who proposed that the energies of any harmonic oscillator, such as the atoms of a blackbody radiator, are restricted to certain values, each of which is an integral (whole number) multiple of a basic minimum value. In 1905 Albert Einstein proposed that the radiation itself is also quantized, and he used the new theory to explain the Photoelectric Effect. Niels Bohr used the quantum theory in 1913 to explain both atomic structure and atomic spectra, showing the connection between the energy levels of an atom's electrons and the frequencies of light given off and absorbed by the atom. Quantum mechanics, the final mathematical formulation of the quantum theory, was developed during the 1920s. In 1924 Louis de Broglie proposed that particles exhibit wavelike properties. This hypothesis was confirmed experimentally in 1927 by Clinton J. Davisson and Lester H. Germer, who observed diffraction of a beam of electrons. Two different formulations of quantum mechanics were presented following de Broglie's suggestion. The wave mechanics of Erwin Schrödinger (1926) involves the use of a mathematical entity, the wave function, which is related to the probability of finding a particle at a given point in space. The matrix mechanics of Werner Heisenberg (1925) makes no mention of wave functions or similar concepts but was shown to be mathematically equivalent to Schrödinger's theory. Quantum mechanics was combined with the theory of relativity in the formulation of P.A.M. Dirac (1928), which also predicted the existence of antiparticles. A particularly important discovery of the quantum theory is the uncertainty principle, enunciated by Heisenberg in 1927, which places an absolute theoretical limit on the accuracy of certain measurements; as a result, the assumption by earlier scientists that the physical state of a system could be measured exactly and used to predict future states had to be abandoned. Other developments of the theory include quantum statistics, presented in one form by Einstein and S.N. Bose (Bose-Einstein statistics, which apply to bosons) and in another by Dirac and Enrico FERMI (Fermi-Dirac statistics, which apply to fermions); quantum electronics, which deals with interactions involving quantum energy levels and resonance, as in lasers; quantum gravitation, the quantum theory of gravitational fields; and quantum field theory. In quantum field theory, interactions between particles result from the exchange of quanta: electromagnetic forces arise from the exchange of photons, weak nuclear forces from the exchange of W and Z particles, strong nuclear forces from the exchange of gluons, and gravitation from the exchange of gravitons. atom atom, the smallest unit of a chemical element having the properties of that element. An atom contains several kinds of particles. Its central core, the nucleus, consists of positively charged particles, called protons, and uncharged particles, called neutrons held together by the strong force. Surrounding the nucleus and orbiting it are negatively charged particles, called electrons. Each atom has an equal number of protons and electrons unless it has been ionized. The nucleus occupies only a tiny fraction of an atom's volume but contains almost all of its mass. Electrons in the outermost orbits determine the atom's chemical and electrical properties. The number of protons in an atom's nucleus is called the atomic number and determines which element it is. The number of nucleons (protons and neutrons in the nucleus) is the atom's mass number. Atoms containing the same number of protons but different numbers of neutrons are isotopes of the element. The atomic weight is the average mass of an atom of an element in atomic mass units. One atomic mass -27 12 unit (1 AMU=1.6606x10 kg) is 1/12th the mass of the C isotope. The atomic weight may involve an average over several naturally occuring isotopes of the element. The mass of atoms other than hydrogen is different from the sum of the masses of the neutrons and protons in the nucleus because of the binding energy of the nucleus. See also history of the atom, standard units. History of the atom History of the atom: In the 5th cent. B.C. the Greek philosophers Democritus and Leucippus proposed that matter was made up of tiny, indivisible particles in constant motion. Aristotle, however, did not accept the theory, and it was ignored for centuries. Modern atomic theory began with the publication in 1808 by John Dalton of his experimental conclusions that all atoms of an element have same size and weight, and that atoms of elements unite chemically in simple numerical ratios (as molecules) to form compounds. In 1911 Ernest Rutherford explained an atom's structure in terms of a positively charged nucleus surrounded by negatively charged electrons orbiting around it. In 1913 Niels Bohr used quantum theory to explain why electrons could remain in certain allowed orbits without radiating energy. The development of quantum mechanics during the 1920s resulted in a satisfactory explanation of all phenomena related to the role of electrons in atoms.