PHYSICS DICTIONARY

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Ordinate

 The Cartesian coordinate obtained by measuring parallel to the y-axis.

Origin

 The point of intersection of coordinate axes as in Cartesian coordinate system

Orthogonal

Having a set of mutually perpendicular axes, meeting at right angles having perpendicular slopes or tangents at the point of intersection.

Oscillation

Type of motion in which object moves about a mean position i.e. fixed point.

Oscillator (Electric)

 Electronic circuit which converts the dc power supply voltage to an output waveform of some frequency. The oscillator circuit is used to generate various waveforms.

 

Osmosis

Diffusion of fluid through a semi permeable membrane from a solution with a low solute concentration to a solution with a higher solute concentration until there is an equal concentration of fluid on both sides of the membrane.

                                                (or)

A process of diffusion of a solvent (such as water) through semi- permeable membrane, which will transmit the solvent but impede most dissolved substances. The normal flow of solvent is from the dilute solution to the concentrated solution.

Ostwald’s Second Law of Thermodynamics

 “Perpetual machine of second kind is impossible”.

 

Outgassing Constant

Rate at which gas appears to emanate from unit area of surface, and is usually measured in units of Torr.liter.sec^-1.cm^-2.

Outgassing

 The emanation of gases from surface of material resulting from desorption.

Oxidation

 The removal of one or more electrons from an atom, ion or molecule.

Ozone

Ozone is an allotrope of oxygen containing three oxygen atoms. The chemical formula for ozone is O₃. Ozone, the first allotrope of any chemical element to be recognized, was proposed as a distinct chemical substance by Christian Friedrich Schönbein in 1840, who named it after the Greek verb ozein ("to smell"), from the peculiar odor in lightning storms. According to experimental evidence from microwave spectroscopy, Ozone is a bent molecule, with C_2v  symmetry (similar to the water molecule).

Ozone Layer Depletion

The ozone layer is located between 10 and 50 km above the Earth's surface and contains 90% of all stratospheric ozone. Under normal conditions, stratospheric Ozone is formed by a photochemical reaction between oxygen molecules, oxygen atoms and solar radiation. The ozone layer is essential to life on earth, as it absorbs harmful ultraviolet-B radiation from the sun. In recent years the thickness of this layer has been decreasing, leading in extreme cases to holes in the layer. Measurements carried out in the Antarctic have shown that at certain times, more than 95% of the ozone concentrations found at altitudes of between 15 and 20 km and more than 50% of total ozone are destroyed, with reductions being most pronounced during winter and in early spring. Natural phenomena, such as sun-spots and stratospheric winds, also decrease stratospheric ozone levels, but typically not by more than 1-2%. The main cause of ozone layer depletion is the increased stratospheric concentration of chlorine from industrially produced Chloro Fluoro Carbons, Halons and selected solvents.

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Non-Conservative Force

If the work done by a force acting on a body depends on path followed then it is called as non-conservative force.

Non-Crystalline

The solid state where in there is no long range atomic order.

Non-Ferrous Alloy

A metal alloy for which iron is not prime constituent.

Non-Inertial Frames of Reference:

The frames relative to which an un-accelerated body appears accelerated are called non-inertial frames. All accelerated frames are non-inertial frames.

Non-Polar Dielectric

It is the substance in which the net electric dipole moment is zero because of its symmetrical structure. The center of gravity of positive and negative charges will coincide.

Normal Distribution

See Gaussian distribution

Normal Force

When two bodies are in contact or when one body is placed over another body, the contact force which either body exerts on other body normal to contact surface is called normal force or normal reaction.

Norton’s Theorem

In a linear network consisting of emfs and resistances when viewed from its output terminals, is equivalent to constant current source with parallel effective resistance. The constant current is equal to current which would flow in a short circuit placed across terminals, and the parallel resistance is resistance of network when viewed from open circuited terminals after all emfs have been removed & replaced by internal resistances.

NTP

Normal temperature and pressure is defined as air at 20^oC (293.15k) and 1atm.

N-Type Semiconductor

A type of semiconductor for which the predominant charge carriers responsible for electrical conduction are electrons.  Normally donor impurity atoms give rise to excess electrons.  

Nuclear Emulsion

Nuclear photographic emulsion, also called Nuclear Emulsion, radiation detector  generally in the form of a glass plate thinly coated with a transparent medium containing a silver halide compound. Passage of charged subatomic particles is recorded in the emulsion in the same way that ordinary black and white photographic film records a picture. After photographic developing, a permanent record of the paths of the charged particles remains and may be observed through a microscope. Radioactivity was discovered in 1896 by its effect on a photographic plate, and nuclear emulsions later played a pivotal role in cosmic-ray research—for example, in the discovery of the Pion in 1947. 

Nuclear Fission

Physical process in which a massive nucleus splits into fragments yielding high energy which gets distributed as kinetic energy of fragments and heat; this is because the sum of masses of fragments will be less than mass of nucleus. If the mass of fragments is equal to or greater than that of iron at peak of binding energy curve, then nuclear particles will be more tightly bound then they were in Uranium nucleus, and that decrease in mass comes off in form of energy according to Einstein equation.

or

It is a type of neutron interaction produced by bombardment of certain very high atomic number nuclei (Z ≥ 92) by thermal or fast neutrons. The target nucleus fragments into two daughter nuclei of lighter mass and the fission process is accompanied with production of fast neutrons. Nuclei that are capable of undergoing fission are called fissionable nuclei in general. Nuclei that undergo fission with thermal neutrons are called fissionable nuclei. Fission fragments combined with the nuclei that are subsequently formed through radioactive decay of fission fragments are called fission products. 

Nuclear Force

It holds nucleons together. It must be very strong since it mostly overcomes Coulomb force. It must have a short range of order 10^-13 cm. It holds the quarks together 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 the Gluon which interacts only with itself and with the quarks.

Nuclear Fusion

Nuclear reaction in which two or more lighter nuclei combine together to form new nucleus. In order to overcome electrostatic interaction for combination of two nuclei, high kinetic energies are required. This is usually achieved by heating matter to very high temperatures leading to plasma state.

Nuclear Magnetron

Any charged particle moving in a closed path produces a magnetic field, which at larger distance acts as due to magnetic dipole located at current loop. The protons inside the nucleus are in orbital motion and therefore produce electric currents which produce extra nuclear magnetic fields. Each nucleon possesses an intrinsic magnetic moment which is parallel to its spin and is probably caused by spinning of nucleon.

Nuclear Physics

The branch of physics which deals with study of internal structure and behavior of nucleus and its constituents. 

Nuclear Reaction

When an atomic nucleus interacts with other nuclei or particle, its structure, mass or energy gets changed. Such a process is referred to as nuclear reaction.

Nuclear Reactor

It is an arrangement used to generate power by utilizing nuclear energy. Fissionable isotopes of Uranium, Plutonium are used as fuel. Heat energy released from fission is used for converting water into steam for driving turbines to generate electricity.

Nuclear Spin

 The total angular momentum of nucleus is usually called nuclear spin.

Nucleon

The charge independence of nuclear interactions suggests that Neutron and Protons are two states of single entity, the nucleon.

Nuclide

Any nuclear species characterized by its atomic number and mass number is called as nuclide. It is conventionally denoted by where ^AX_Z; X is symbol of element; ‘A’ is mass number and ‘Z’ is called as atomic number

Nutation

The rise and fall of axis of rotation about its position of dynamic equilibrium is called as Nutation.      

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Newton’s Universal Law of Gravitation

Every two bodies in the universe attract each other with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between the masses.

Newtonian Fluids

Fluids which obey Newton’s law of viscosity are called Newtonian fluids. It is a fluid whose viscosity doesn’t change with rate of flow.

Newtonian Telescope

It is telescope designed by Sir Isaac Newton which uses two mirrors to bring light to a focus. Light from object being viewed is collected by concave primary mirror and reflected to a smaller secondary flat plane mirror. The flat mirror is inclined at 45^o to axis of telescope and reflects light to an eye lens which forms an image.

Nicol Prism

It is a special kind of a prism made of natural crystal, which is used to obtain plane polarized light from an un-polarized light and it is also used for analysis of a given light.

NIM Layout

A complete NIM system consists of a NIM crater, NIM bin and NIM modules. A typical NIM crate has 12 slots for insertion of modules. The communication and data transfer between the modules is realized through a built-in backplane. One of the deficiencies of the standard NIM backplane is that it does not have a digital data bus to allow computer based control. However some of the modern NIM modules have built-in communication ports, which allow them to be controlled and read out through a computer. A standard NIM crate has a built-in power supply that draws power from 110V or 240V AC outlets. Crates having other specific input voltage ratings are also

available. The DC voltages are generated within the crate, that is, no extra DC supply module is needed. The voltages are distributed through the backplane and are also available in front of the crate for other user-specific requirements.

NIM Modules

A standard NIM module has a height of 8.75 inches. The width of the module can be variable but it must be a multiple of 1.35 inches. The pin layout of a standard NIM module is a mirror image of the NIM crate connector assignments. Both front and rear sides of a typical NIM module also contain a number of connectors to facilitate different I/O operations. Some of the modern NIM modules also contain communication ports (such as RS232) to allow control and readout through a computer. These ports are necessary due to unavailability of digital data bus in NIM crates. As mentioned earlier, NIM modules are well suited for small scale systems that do not require complicated data handling and control.

NIM Standard

Nuclear Instrumentation Methods (NIM) is an old standard that came into effect in 1964. The basic idea behind its establishment was to introduce standalone and replaceable modules, which could be combined together to form a complete data acquisition system. The convenience of using modules interchangeably without disturbing other parts of the system has been the main source of its widespread use by physicists and engineers. Even though new standards and modular systems have been introduced but due to its simplicity of integration and use, NIM is still used in many places.

Nuclear Magnetic Resonance (NMR)

Nuclear magnetic resonance (NMR) was first developed in 1946 by research groups at Stanford and M.I.T., in the USA. NMR is the phenomenon of absorption of electromagnetic radiation of a specific frequency by an atomic nucleus that is placed in a strong magnetic field, used especially in spectroscopic studies of molecular structure and in medicine to measure rates of metabolism.

Node

Position of a materialistic wave where positions, displacement, amplitude, velocity and acceleration are zero, but strain is maximum. Nodes are equivalent in a wave.

No Equilibrium (Radioactive Decay)

It is condition of radioactive decay which occurs if the half life of parent is less than the half life of daughter i.e. activity due to parent nuclide will diminish quickly as it decays into the daughter. Consequently the net activity will be solely determined by the activity of the daughter.

Noise (Sound)

Sound that produces jarring effect or displeasing effect on ear is called a noise. The noise succeeds at irregular intervals and there is sudden change in loudness.

                                        or

A non periodic mechanical disturbance produces sound which appears unpleasant to ear. It is irregular, non- periodic and discontinuous mechanical substance.

Non-Inertial Frame of Reference

A reference frame in which Newton’s laws are not valid in their original forms is called as non-inertial frame. Any accelerating frame or a rotating frame is non-inertial frame.

Non-Linear Regression

By nonlinear regression we mean fitting any nonlinear function to the data. This could be a polynomial of the order 2 or more, an exponential, a logarithmic, a combination of these, or some other function. There are different techniques available to handle the nonlinear regression problems but the two most practical and common ones are least squares regression and maximum likelihood regression. 

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Moon

The moon is Earth's only natural satellite. The moon is a cold, dry sphere whose surface is studded with craters and strewn with rocks and dust (called regolith). The moon has no atmosphere. The moon is about 238,900 miles (384,000 km) from Earth on average. The moon's diameter is 2,159 miles (3,474 km), 27% of the diameter of the Earth. The moon's mass is (7.35 x 10 22 kg), about 1/81 of the Earth's mass. The moon's gravitational force is only 17% of the Earth's gravity. The moon's density is 3340 kg/m 3. This is about 3/5 the density of the Earth. 

Moseley’s Law

The frequency of a spectral line in characteristic X-ray spectrum varies directly as square of atomic number ‘Z’ of the element emitting it.

Moseley’s Law for X-rays

The frequency of a spectral line in characteristic X-ray spectrum varies directly as square of atomic number Z of element emitting it.

Mosley’s Experiment

Mosley in 1913 carried out a systematic study of K_α X-rays produced by elements from aluminum to gold using Bragg technique of X-rays scattering from a crystalline lattice of a potassium ferro-cyanide crystal. The characteristic K_α X-rays were produced by bombardment of targets with energetic electrons. The results of Mosley’s experiments confirmed the Bohr’s atomic theory. 

Mossbauer Effect

Rudolf Mossbauer, in 1958, discovered the recoil-free emission and absorption of gamma rays by nuclei. The Mossbauer effect states that when some atoms are held tightly in crystalline atomic structures, the gamma radiation emitted by their nuclei are very close to being recoil-free.  This implies that the emitted photon has the exact frequency that corresponds to the transition energy between the nuclear ground state and the excited state.  When this photon carrying the full nuclear transition energy strikes another similar nucleus also embedded in a tight crystalline structure, absorption may occur.  Because the nuclear energy levels are very sharply defined, only such a photon - one that carries the exact transition energy - may excite another nucleus. Because of the very narrowly defined nuclear energy states, the smallest change in the energy of the photon will destroy the resonance.  Thanks to this extreme sensitivity, Mossbauer spectroscopy has proven itself an excellent method to measure otherwise impossible to detect nuclear energy differences.  Minuscule energy variations, magnetic fields at the nucleus, and even distortions or asymmetries in the shape of the lattice that encloses the atom are enough to produce shifts and split tings in the absorption line.  All these alterations of the nuclear environment that produce an observable effect are called the nuclear hyperfine interactions.  

Most Probable Speed

It is the speed possessed by maximum number of molecules in a gas sample.

Motion

Change in position of an object with respect to time seen by an observer from a frame of reference.

Multiwire Drift Chamber

A multiwire drift chamber is a tracking device that was built to track particles in high energy physics collisions. It uses the timing information to determine the position of an ionizing particle. In a drift chamber the cathode is made up of either closely spaced wires or strips that are kept at distributed potentials. The advantage of this design is that the electrons produced by the incident radiation are directed towards the nearest anode wire with a constant drift velocity. The incident radiation produces electron ion pairs inside the active volume that drift towards the nearest anode and cathode. After passing through the chamber, the radiation is detected by a fast detector, such as scintillation counter, which produces a pulse. This pulse initiates a logic-enable pulse that starts a timing counter. The counter keeps on counting until it gets a stop signal that is generated when the electrons eventually reach the anode, produce avalanche, and produce an anode pulse. The number of ticks of the counter determines the time it has taken the electrons to reach the anode wire. Now, if the drift velocity of the electrons in the chamber gas is known, one can determine the distance traveled by the electron and hence position at which the electron was produced by the radiation.

Muon

It is an elementary particle, a lepton having spin ½ and about 200 times the mass of electron. It is usually formed from decay of Pion.  

Muonic Atom

It is an atom in which an electron is replaced by a negative muon orbiting close to or within the nucleus. Muonic atom consisting of a proton and negative with a reduced mass of 186 Me.   

Muonium (Mu)

It is a light, Hydrogen like neutral atom consisting of a positive muon μ⁺ and an orbital electron. Chemists consider Muonium to be a light unstable isotope of Hydrogen. It is formed when an energetic positive Muon slows down in an absorber and attracts an electron which then revolves about Muon. The reduced mass of Muon is within 0.5% of electron mass.

Musical Interval

The ratio of frequencies of two tones is called musical interval.

Musical Scale

If several tones in increasing order of their frequencies are arranged in a series such that they have a definite musical interval and their resultant effect is pleasant to the ear, it is called the musical scale.

Mutual Induction

When two coils are placed near each other such that the current flowing in one changes, emf is induced in the second coil. Such phenomenon is known as mutual induction. 

Myopia

Term used for short sight. Light from a distant object forms an image before it reaches retina. A myopic person has clear vision when looking objects close to them but distant objects will appear blurred.