Реферат: Физические законы, переменные, принципы
Magnus effect
A rotating cylinder in a moving fluid drags some of the fluidaround with it, in its direction of rotation. This increases thespeed in that region, and thus the pressure is lower.Consequently, there is a net force on the cylinder in thatdirection, perpendicular to the flow of the fluid. This is calledthe Magnus effect.
Malus's law (E.L. Malus)
The light intensity travelling through a polarizer is proportionalto the initial intensity of the light and the square of the cosineof the angle between the polarization of the light ray and thepolarization axis of the polarizer.
Maxwell's demon (J.C. Maxwell)
A thought experiment illustrating the concepts of entropy. Wehave a container of gas which is partitioned into two equal sides;each side is in thermal equilibrium with the other. The walls(and the partition) of the container are a perfect insulator. Now imagine there is a very small demon who is waiting at thepartition next to a small trap door. He can open and close thedoor with negligible work. Let's say he opens the door to allow afast-moving molecule to travel from the left side to the right, orfor a slow-moving molecule to travel from the right side to the left, and keeps it closed for all other molecules. The net effectwould be a flow of heat -- from the left side to the right -- eventhough the container was in thermal equilibrium. This is clearlya violation of the second law of thermodynamics. So where did we go wrong? It turns out that information hasto do with entropy as well. In order to sort out the moleculesaccording to speeds, the demon would be having to keep a memory ofthem -- and it turns out that increase in entropy of the simplemaintenance of this simple memory would more than make up for thedecrease in entropy due to the heat flow.
Maxwell's equations (J.C. Maxwell; 1864)
Four elegant equations which describe classical electromagnetismin all its splendor. They are:
Gauss' law. The electric flux through a closed surface is proportional to the algebraic sum of electric charges contained within that closed surface.
Gauss' law for magnetic fields. The magnetic flux through a closed surface is zero; no magnetic charges exist.
Faraday's law. The line integral of the electric flux around a closed curve is proportional to the instantaneous time rate of change of the magnetic flux through a surface bounded by that closed curve.
Ampere's law, modified form. The line integral of the magnetic flux around a closed curve is proportional to the sum of two terms: first, the algebraic sum of electric currents flowing through that closed curve; and second, the instantaneous time rate of change of the electric flux through a surface bounded by that closed curve.
In addition to describing electromagnetism, his equations alsopredict that waves can propagate through the electromagneticfield, and would always propagate at the same speed -- these are electromagnetic waves.
Meissner effect (W. Meissner; 1933)
The decrease of the magnetic flux within a superconducting metalwhen it is cooled below the critical temperature. That is,superconducting materials reflect magnetic fields.
Michelson-Morley experiment (A.A. Michelson, E.W. Morley; 1887)
Possibly the most famous null-experiment of all time, designed toverify the existence of the proposed "lumeniferous aether" throughwhich light waves were thought to propagate. Since the Earthmoves through this aether, a lightbeam fired in the Earth'sdirection of motion would lag behind one fired sideways, where noaether effect would be present. This difference could be detectedwith the use of an interferometer.
The experiment showed absolutely no aether shift whatsoever,where one should have been quite detectable. Thus the aetherconcept was discredited as was the constancy of the speed oflight.
Millikan oil drop experiment (R.A. Millikan)
A famous experiment designed to measure the electronic charge.Drops of oil were carried past a uniform electric field betweencharged plates. After charging the drop with x-rays, he adjustedthe electric field between the plates so that the oil drop wasexactly balanced against the force of gravity. Then the charge onthe drop would be known. Millikan did this repeatedly and foundthat all the charges he measured came in integer multiples only ofa certain smallest value, which is the charge on the electron.
Newton's law of universal gravitation (Sir I. Newton)
Two bodies attract each other with equal and opposite forces; themagnitude of this force is proportional to the product of the twomasses and is also proportional to the inverse square of thedistance between the centers of mass of the two bodies.
Newton's laws of motion (Sir I. Newton)
Newton's first law of motion. A body continues in its state of rest or of uniform motion unless it is acted upon by an external force.
Newton's second law of motion. For an unbalanced force acting on a body, the acceleration produces is proportional to the force impressed; the constant of proportionality is the inertial mass of the body.
Newton's third law of motion. In a system where no external forces are present, every action is always opposed by an equal and opposite reaction.
Ohm's law (G. Ohm; 1827)
The ratio of the potential difference between the ends of aconductor to the current flowing through it is constant; theconstant of proportionality is called the resistance, and isdifferent for different materials.
Olbers' paradox (H. Olbers; 1826)