PHYSICS DICTIONARY

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Stiffness Constant

Any one of the coefficients of the relations in the generalized Hooke's law used to express stress components as linear functions of the strain components.

Stimulated Emission (LASER)

If in the excited state of the atom, a photon of frequency same as the frequency of photon which the atom in passing from the excited state to the ground state will emit, strikes the atom, then that atom come to ground state very soon and stimulates the light incident on it, by emitting photon of exactly the same frequency. This is called stimulated emission.

Stochastic Process

Stochastic process appears in probability theory, a process involving the operation of chance. For example, in radioactive decay every atom is subject to a fixed probability of breaking down in any given time interval. More generally, a stochastic process refers to a family of random variables indexed against some other variable or set of variables.

Stoichometry

The word stoichometry derives from two Greek words:  Stoicheion (meaning "element") and Metron (meaning "measure"). Stoichometry deals with calculations about the masses (sometimes volumes) of reactants and products involved in a chemical reaction. It is a very mathematical part of chemistry. The rules for determining stoichometric relationships are based on the laws of conservation of mass and energy and the law of combining weights or volumes.

Stokes Lines

The smaller frequency component in Raman spectrum are called stokes lines.

Stopping Power

The ratio of differential energy loss within the absorber to the corresponding differential path length for a charged particle is called stopping power.

or

Stopping power or linear energy transfer (LET) is the energy lost per unit path length.

STP (Standard Temperature Pressure)

 STP is commonly used to define standard conditions for temperature and pressure which is important for measurements of chemical and physical processes. As per IUPAC (International Union of Pure and Applied   Chemistry), it is defined as air at 0 oC and 105 Pascals. STP in imperial and USA system of units is defined as air at 60oF and 14.696 Psi.

Straggling

Energy lost by identical charged particles passing through a medium is statistical in nature if the medium is inhomogeneous in nature, this would lead to variation in “range” of same energetic incident particles in that medium. This is called straggling.

Strain (Engineering)

 The change in gauge length of a specimen (in the direction of an applied stress) divided by its original gauge length.

Strain Energy

When a body is deformed, the work done is stored in the form of potential energy in the body. This potential energy is called strain energy.

Strange Particles

Kaons (K-mesons) and Hyperons are known as strange particles. They are produced in strong interactions but they decay slowly and are hence called as strange particles.

Stratopause

The boundary between the stratosphere and the mesosphere is called the stratopause.

Stratosphere

The stratosphere is a layer of Earth's atmosphere. The stratosphere is the second layer, as one move upward from Earth's surface, of the atmosphere. The stratosphere is above the troposphere and below the mesosphere. The top of the stratosphere occurs at 50 km (31 miles) altitude. 

Stream Line Flow

It is the path of liquid such that tangent to which at any point gives the direction of flow of liquid at real point.

or

When a liquid flows such that each particle of liquid passing a point moves along the same path and has some velocity as preceding particle, its flow is called streamline flow.

Stress

Restoring force per unit area.

Strong Interaction

Interaction which exists between nucleons and holds them is called as strong interaction. This interaction overcomes Coulomb’s force. It has short range of order of 10-13 cm. It holds quarks together in the Proton and Neutron and also holds protons and neutrons together in nucleus of an atom. The strong interaction force is carried by spin -1 particle called Gluon which interacts only with itself and with quarks.

Strong Nuclear Force

The force which holds nucleus together. It has short range of order 10-13 cm. It holds quarks together in the proton and neutron and also holds protons and neutrons together in nucleus of an atom. It is believed that this force is carried by another spin -1 particle called Gluon which interacts only with itself and with the quarks. 

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