PHYSICS DICTIONARY

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Soldering

 It is a method of using a filler metal for joining two metals without heating them to melting points.

or

The American welding society defines soldering as metal coalescence below 800^oF. Soldering is a process in which two adjoining metal surfaces are bonded by means of wetting the metal surfaces completely with molten filler material.

Solenoid

A solenoid is a coil of insulated or enameled wire wound on a rod-shaped form made of solid iron, solid steel, or powdered iron. Devices of this kind can be used as electromagnets, as inductors in electronic circuits.

Solid state physics

Branch of physics which deals with study of formation of crystal structures, mechanical & electrical properties of solids.

Solubility limit

The maximum concentration of solute that may be added without forming a new phase is called as solubility limit.

Solute

 The constituent present in relatively small amounts is called solute.

Solution

 It is a homogenous mixture of a single phase containing one or more chemical species dispersed on a molecular scale.

Solvent

 The constituent of solution present in largest amount is called solvent.

SONAR (Sound Navigation And Ranging)

It is a device used to find depth of a sea or to locate the underwater objects like iceberg, submarine, shoals of fish etc. it consists of two parts; a transmitter which emits the ultrasound waves in all directions and a receiver which detects reflected ultrasound wave.

Sonic boom

Sound generated by an object like plane travelling through air higher than speed of sound. If plane is flying faster than sound, then the pressure waves are left behind. As they spread outwards from the points at which they were formed along the flight path, they become concentrated at the edge of a cone. This reaches right down to ground, where we hear a sonic boom.

Sorption

The taking up and holding of one substance by another. Sorption includes the processes of absorption and adsorption.

Sound

 Distance per unit time.

Spallation

Spallation is generally defined as fragmentation of a target into many smaller components as a result of impact or stress. Consequently nuclear spallation is defined as disintegration of a target nucleus. Spallation is defined as disintegration of a target nucleus into many small residual components such as alpha particles and nucleus upon bombardment with a suitable projectile such as light or heavy ion beams or neutrons. Nuclear spallation also occurs naturally in earth’s atmosphere as a result of exposure of nuclides to energetic cosmic rays such as protons.

For instance, ₈O¹⁶ + n -----à 3α+ 2p+3n.

Spallation can be used for production of radio nuclides and for generation of neutron beams in spallation neutron generators.

Spark Chamber

A spark chamber is a construction of metal plates placed in a sealed box. A high voltage is applied between the plates and since they are close to each other, it creates a big electric field. The plates are placed in a sealed box which is filled with gas. The basic idea of the detector is simple. The travelling particle will ionize the gas between the plates. Using a triggering system, the high voltage is applied to the plates immediately after the particle went through the chamber. This produces sparks on the exact trajectory of the particle. The triggering system is made of two scintillators coupled with a photomultiplier tube, one on top of the chamber and the other below it. Observations are made for coincidences between the two scintillators. When a coincidence is observed, a pulse is sent to a spark gap. It triggers a capacitor to discharge itself in the chamber. Then, the data acquisition system plays its role.

Spatial Coherence

 Coherence between the waves from coherent source travelling side by side at some separation is called spatial coherence.

Special Theory of Relativity

It is the theory proposed by Einstein. The postulates are as follows:

i) the fundamental laws of physics have the same form in all inertial systems.

ii) The velocity of light in vacuum is independent of the relative motion of source and observer.

Specific Activity

Radio activity per unit mass of a radio nuclide.

Specific Charge

The ratio of charge to mass of an elementary particle is called as specific charge. 

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Short Circuit

It is a path in electric circuit, whereby there is almost no resistance to the current in that path.

SI System of Units

The currently used metric system of units is known as systeme international of ‘unite’s (International system of units) with international abbreviation SI. The system is founded on base units for seven basic physical quantities. All other quantities and units are derived from the seven base quantities and units.

 

The seven base quantities and their units are

 

Length ‘l’ --- Meter (m)	Mass ’M’ --- Kilogram (Kg)
Temperature (T) --- Kelvin (k);	Luminous intensity -- Candela (cd)
Time (t) --- second(s)	Electric current (I) --- Ampere (A)
Amount of Substance --- mole (mol)

Siemens

It is an alternative name for Mho. It is SI unit of electrical conductance and equal to one ampere per volt.

Sievert

Unit of dose equivalent when dose ‘D’ is measured in Grays

Signal-to-Noise Ratio

Signal-to-Noise ratio is one of the most widely used parameters to characterize detector response. As the name suggests, it is given by the ratio of the signal to noise.

Silsbee Effect

 If the magnetic field produced by current carrying super conductors exceeds critical value, the material loses superconductivity and becomes normal. This phenomenon is called Silsbee effect named after its discoverer.

Simple Harmonic Motion

It is type of motion where the acceleration is directed towards a fixed point (mean position of rest) and is proportional to the displacement of vibrating particle.

Simple Pendulum

 An arrangement of a heavy particle suspended by means of a weightless inextensible, flexible string from a rigid support making simple harmonic oscillation about mean position.

Simulator

Sin(angle of incidence)/Sin(angle of refraction) = refractive index (medium).

Single Crystal

 A crystal in which there is periodic arrangement and repeated arrangement of atoms exists throughout the crystal without any disturbance. All unit cells interlock in same fashion and have same orientation.

Sintering

Particle coalescence of a powdered aggregate by diffusion that is accomplished by fixing at an elevated temperature is called as sintering.

Sinusoidal Function

Function having mathematical form given by Asin(2pft); where ‘A’ is the amplitude of the wave, ‘f’ is its frequency and ‘t’ is time.

Sinusoidal Oscillator

 Electronic device which produces sine waves.

Sinusoidal or Sine Wave

A sine wave is a repetitive change or motion which, when plotted as a graph, has the same shape as the sine function.

Siren

A device in which compressed air or steam is driven against a rotating perforated disk to create a loud sound as a signal or warning.

Skin Depth

The depth inside the conductor at which the amplitude of electromagnetic decreases by a factor 1/e. It is measure of depth to which an Electromagnetic wave penetrates.

Skin Effect

When an alternating current of high frequency flows through the conductor, current density is not uniform throughout the crossectional area. Current density is more near the surface than inside the conductor. High frequency alternating current is confined to surface layer. The phenomenon is called as “skin effect”.

Slip

 Plastic deformation as the result of dislocation motion, also the shear displacement of two adjacent planes of atoms.

Smoke

Smoke is a collection of a airborne  solid  and  liquid  particulates  and gases emitted when a material undergoes  combustion  together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires. 

 

Snell’s Law

An empirical relationship formulated by Willeboard Snell around 1621, which is used to describe the relationship between the angles of incidence and refraction, when referring to light or other waves passing through a boundary between two different isotropic media. Snell's law states that the ratio of the sine of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the reciprocal of the ratio of the indices of refraction.

Solar Day

A solar day is the time it takes for the Earth to rotate about its axis so that the sun appears in the same position in the sky. 

Solar Eclipse

As seen from the Earth, a solar eclipse is a natural phenomenon which occurs when the Moon passes between the Sun and Earth, and the Moon fully or partially blocks ("occults") the Sun. 

Soft Magnetic Material

A ferromagnetic or ferrimagnetic material having small B vs H hysteresis loop, which may be magnetized and demagnetized with relative ease.

Soft Radiation

Term usually attributed to X-ray radiation or other particles or photons having very low energy, and, as a result, do not penetrate any type of material easily.

Softening Point (Glass)

The maximum temperature at which a glass piece may be handled without permanent deformation; this corresponds to a viscosity of approximately 4x10⁶ Pa.Sec

Solar Cell

 A solar cell is a PN junction in which generation of carriers by an external source of energy, usually sunlight is utilized to generate electrical power. Solar cell operation is based on generation of electron – hole pairs in transition region, and the separation of both types of carriers by the junction electric field.

Solar Constant

 It is the amount of radiant energy received from the sun by the earth per unit area per unit time normally at the mean distance of earth from the sun. The numerical value is 1.388 x 10³ Wm².

Solar Day

Time taken by the moon to complete one rotation around the earth.

Solar Wind

The corona, the sun's outer layer, reaches temperatures of up to 2 million degrees Fahrenheit (1.1 million Celsius). At this level, the sun's gravity can't hold on to the rapidly moving particles, and it streams away from the star. The solar wind is a stream of energized, charged particles, primarily electrons and protons, flowing outward from the Sun, through the solar system at speeds as high as 900 km/s and at a temperature of 1 million degrees (Celsius). It is made of plasma. 

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Seebeck Effect

If two junctions of dissimilar conductors in a circuit are held at different temperatures, an emf develops causing a current to flow in the circuit. The thermoelectric emf V_AB for two materials A and B is V_A-V_B , where V_A and V_B are characteristic of materials A and B respectively. This implies V_AB - V_CB.

Seismic Waves

 From the focus, shock waves spread out through the earth known as seismic waves.

Seismogram

A record by a seismograph on a display screen or paper print out.

Seismograph

An instrument that makes a record of seismic waves caused by earthquakes. Seismographs are equipped with electromagnetic sensors that translate ground motions into electrical charges, which are processed and recorded by instruments; analog or digital circuits.

Seismology

Seismology is the branch of science that deals with earthquakes, their effects, the movement of the Earth's tectonic plates, and prediction of earthquakes.

Selection Rules

The rules connecting the characteristics of the transition in terms of change in angular momentum and parity, with the transition order, are called as “selection rules”.

Self Diffusion

 Atomic migration in pure metals.

Self Induction

The property of the circuit by virtue of which any change in current in it hence change in magnetic flux in it, induces an emf in it is called as self induction.

Self Powered Neutron Detector (SPND)

In very large reactor plants, the need exists to monitor neutron flux in various portions of the core on a continuous basis. This allows for quick detection of instability in any section of the core. This need brought about the development of the self-powered neutron detector that is small, inexpensive, and rugged enough to withstand the in-core environment. The self-powered neutron detector requires no voltage supply for operation.

                The central wire of a self-powered neutron detector is made from a material that absorbs a neutron and undergoes radioactive decay by emitting an electron (beta decay). Typical materials used for the central wire are cobalt, cadmium, rhodium, and vanadium. A good insulating material is placed between the central wire and the detector casing. Each time a neutron interacts with the central wire it transforms one of the wire’s atoms into a radioactive nucleus. The nucleus eventually decays by the emission of an electron. Because of the emission of these electrons, the wire becomes more and more positively charged. The positive potential of the wire causes a current to flow in resistor, R. A milli voltmeter measures the voltage drop across the resistor. The electron current from beta decay can also be measured directly with an electrometer.

Semiconductor

 Solids which have conductivity less than metals but more than that of insulators are classified as semiconductors. In terms of energy band structure, at 0K, completely filled valence band separated from empty conduction band by a relatively narrow forbidden gap generally less than 2eV. 

Sextant

A navigational instrument containing a graduated 60-degree arc, used for measuring the altitudes of celestial bodies to determine latitude and longitude is called as sextant.

Shadow

A shadow is a dark shape on a surface that is made when something stands between a light and the surface.

or

An area that is not or is only partially irradiated or illuminated because of the interception of radiation by an opaque object between the area and the source of radiation is called as shadow.

Shake

 It is smallest unit of time; 1shake = 10^-8 sec.

Shear

A force applied so as to cause or tend to cause two adjacent parts of same body to slide relative to each other in a direction parallel to their plane of contact.

Shearing Strain

It is the ratio of relative displacement between two layers of the body to the normal distance between those two layers. It can be expressed as the angle through which line originally normal to the fixed surface is turned.

Shell Model

A shell model is one in which the system is thought to consist of individual particles moving in bound orbitals in response to the remainder of the system.  Each orbital has a well designated energy, angular momentum, and parity associated with it.  In an atom, the electrons are bound to the highly charged nucleus, which contains most of the mass of the atom, by the electric force.  Since most of the mass is contained in the nucleus, the electrons can move in orbits relatively free of any obstacles and hence would suffer very few collisions in their eternal orbiting about the nucleus.  In such a model, treated quantum-mechanically, no two electrons, two protons, or two neutrons can occupy the same quantum state, i.e. have identical sets of quantum numbers.  This principle attributed to Pauli results in a finite number of such particles occupying a given energy level, and thus, leads to the concept of closed (or filled) levels (or shells).  When a shell is filled, any additional particles of that type must be put in a different level (shell).