Реферат: Физические законы, переменные, принципы
For steady-state heat conduction in one dimension, the temperaturedistribution is the solution to Laplace's equation, which statesthat the second derivative of temperature with respect todisplacement is zero.
Laue pattern (M. von Laue)
The pattern produced on a photographic film when high-frequencyelectromagnetic waves (such as x-rays) are fired at a crystallinesolid.
Laws of conservation
A law which states that, in a closed system, the total quantity ofsomething will not increase or decrease, but remain exactly thesame. For physical quantities, it states that something canneither be created nor destroyed.
The most commonly seen are the laws of conservation of mass-energy (formerly two conservation laws before A. Einstein), ofelectric charge, of linear momentum, and of angular momentum.There are several others that deal more with particle physics,such as conservation of baryon number, of strangeness, etc., whichare conserved in some fundamental interactions but not others.
Law of reflection
For a wavefront intersecting a reflecting surface, the angle ofincidence is equal to the angle of reflection.
Laws of black hole dynamics
First law of black hole dynamics. For interactions between black holes and normal matter, the conservation laws of total energy, total momentum, angular momentum, and electric charge, hold.
Second law of black hole dynamics. With black hole interactions, or interactions between black holes and normal matter, the sum of the surface areas of all black holes involved can never decrease.
Laws of thermodynamics
First law of thermodynamics. The change in internal energy of a system is the sum of the heat transferred to or from the system and the work done on or by the system.
Second law of thermodynamics. The entropy -- a measure of the unavailability of a system's energy to do useful work -- of a closed system tends to increase with time.
Third law of thermodynamics. For changes involving only perfect crystalline solids at absolute zero, the change of the total entropy is zero.
Zeroth law of thermodynamics. If two bodies are each in thermal equilibrium with a third body, then all three bodies are in thermal equilibrium with each other.
Lawson criterion (J.D. Lawson)
A condition for the release of energy from a thermonuclearreactor. It is usually stated as the minimum value for theproduct of the density of the fuel particles and the containmenttime for energy breakeven. For a half-and-half mixture ofdeuterium and tritium at ignition temperature, nG t is between1014 and 1015 s/cm3 .
Le Chatelier's principle (H. Le Chatelier; 1888)
If a system is in equilibrium, then any change imposed on thesystem tends to shift the equilibrium to reduce the effect of thatapplied change.
Lenz's law (H.F. Lenz; 1835)
An induced electric current always flows in such a direction thatit opposes the change producing it.
Loschmidt constant; Loschmidt number; NL
The number of particles per unit volume of an ideal gas atstandard temperature and pressure. It has the value 2.68719. 1025 m-3.
Lumeniferous aether
A substance, which filled all the empty spaces between matter,which was used to explain what medium light was "waving" in. Nowit has been discredited, as Maxwell's equations imply thatelectromagnetic radiation can propagate in a vacuum, since theyare disturbances in the electromagnetic field rather thantraditional waves in some substance, such as water waves.
Lyman series
The series which describes the emission spectrum of hydrogen whenelectrons are jumping to the ground state. All of the lines arein the ultraviolet.
Mach's principle (E. Mach; 1870s)