PHYSICS DICTIONARY

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Object

 Matter which is tangible and can be described by attributes like mass.

Oblate

Word attributed to “Having shape of spheroid generated by rotating an ellipse about its shorter axis.”

or

“Having an equatorial diameter greater than distance between poles, flattened at poles.”

Octave

 Name given to musical interval with ratio of frequency as 2:1.

Odd-Even Nucleus

 Nucleus having odd number of protons and even number of neutrons.

Odd-Odd Nucleus

 Nucleus having odd number of protons and odd number of neutrons.

Oersted

It is CGS unit of magnetic field strength. It is equal to force of one dyne acting upon a unit magnetic pole placed in magnetic field in vacuum. It is equal to 79.577 amperes per meter.

 

Ohm

 Unit used for resistance.

Ohm’s Law

 At constant temperature, the potential difference across a conductor is directly proportional to current through it.

Ohmic Conductor

Conductors which obey ohm’s law are called as Ohmic conductors. They always have positive slope in I-V characteristic graph.

Ohmmeter

 Device used to measure resistance.

Opacity

 Property by which body obstructs light transmission by absorption or reflection. It determines the degree of opaqueness.

Opaque

Being impervious to the transmission of light as a result of absorption, reflection and or scattering of incident light.

Open System

 It is defined as a system which exchanges both energy and matter with surroundings.

Optical Bench

An apparatus fitted with light source, lenses, prism and other optical devices, for observation and measurement of optical phenomenon.

Optical Density

It is measure of extent to which the medium transmits light or electromagnetic wave of particular wave length.

or

The degree to which a refractive medium refracts transmitted rays of light.

Optical Fiber

 A very thin transparent fiber made of glass used to transmit light over long distances without much attenuation. They are surrounded by transparent cladding material with lower refractive index. Light is kept in fiber by total internal reflection.

Optics

Branch of physics which deals with generation, transmission of light, interaction of light with matter, instruments used for detection of light and devices used to eliminate aberrations in images formed by optical instruments.

Optoelectronics

It is branch of electronics which deals with theory, design, manufacture and operation of electronic devices that converts electrical signal to visible or infrared radiations or from light to electro signal.

or

The stored energy which is not apparently shown by a system is called internal energy or intrinsic energy.

Orbital Gyromagnetic Ratio

The ratio of magnetic dipole moment of the electron due to its orbital motion is called orbital gyromagnetic ratio.

Orbital Velocity

 It is velocity of body revolving around the earth in an orbit. It is independent of mass of orbiting body and it will be always along the tangent to the orbit at any point.

Ordinary Ray

One of the two refracted rays obtained from double refracting crystal, which obeys laws of refraction.

PHYSICS DICTIONARY

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Nano Materials

Materials whose dimensions are less than 100 nm.

Natural Frequency

 Frequency of system when set in free vibration.

Natural Logarithm

A logarithm to the base ‘e’ which is irrational and whose value is equal to 2.71829. It is represented as log _eX_.. It is also called as Napier logarithm.

Nebula

 A visible, thinly spread cloud of interstellar gas and dust. Some nebulae are remnants of supernova explosion others are gravity induced condensations of gases in interstellar medium which in certain cases may become a site for formation of new stars. The term was formerly used of any hazy , seemingly cloud like object, including what are now recognized as other galaxies beyond milky way, it is restricted now to actual clouds of gas and dust within our own galaxy.

Negative Feedback

When feedback energy is out of phase with input signal and opposite to it, then it is called negative effect.

Negatron

Term used for electron when it is necessary to distinguish between electrons and positrons.

Neptunium Series

It is a radioactive series that does not now occur in nature and that begins with Plutonium of mass number-241 and continues to Americium to the longer lived member of series i.e. Neptunium of mass number 237, and eventually to stable end product Bismuth. 

Neutrino

An elementary particle introduced by Pauli in 1952. It was introduced in weak interactions involving beta decay to avoid violation of law of conservation of energy and angular momentum. It has solved mystery of variable energy of beta particles in beta decays.

 

Neutron Diffraction

 It is a non destructive technique that is used to probe the structure of materials at the atomic level. The sample is placed within a neutron beam and the angles at which the neutrons are deflected or scattered by material are recorded to generate a  “diffraction pattern” from which structural information can be extracted. Diffraction occurs when the neutrons encounter atomic nuclei or magnetic diploes within the sample. With an effective wavelength of 0.1-20 nm, thermal neutrons are ideally suited for probing atomic scale structures with high resolution. As neutrons do not possess an electric charge, they readily pass through matter regardless of local charge distribution. In consequence, a neutron beam is capable of penetrating well beyond surface of a sample, to a depth of few centimeters in most condensed phases. The technique is widely used in engineering for stress mapping and to examine mechanical behavior of materials and engineering components.

Neutron Flux

The neutron flux (φ) measures the intensity of neutrons passing through a cubic centimeter of material. It is given by: φ= nv; where n is the density of neutrons (the number of neutrons per cm3) and v is the speed of the neutrons. The unit for neutron flux is neutrons.cm^-2.sec^-1.

In physical terms, the quantity ‘φ’ is the total distance traveled in one second by all the neutrons in the one cm³ volume, since it is obtained by multiplying the number of neutrons in that cm³ by the speed each is travelling. This is equivalent to the total length of all the neutron tracks laid down in one cm³ in one second. The expression for neutron flux applies to any neutron energy. When applied to thermal neutrons the product is known as the thermal neutron flux.  

Newton

It is SI unit of force. It is force required to accelerate a mass of one kilogram one meter per second per second. 

Newton’s First Law

Everybody continues in its state of rest or of uniform motion in a straight line unless it is compelled by an external force to change that state.

Newton’s Law of Cooling

The rate of loss of heat of a hot body (or rate of cooling of body) is directly proportional to mean excess of temperature of hot body over that of its surroundings.

Newton’s Second Law

The rate of change of momentum of a body is directly proportional to external force acting on it and takes place in the direction of force.

Newton’s Third Law

For every action, there is equal and opposite reaction.

 

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Macroscopic

Large enough to be perceived or examined by naked eye.

(or)

Anything which is considered for bulk of matter as a whole.

Magnetic Dipole

An object such as current loop, an atom or a bar magnet, that experiences torques due to magnetic forces. 

Magnetic Field Intensity

It is measured by force acting on unit magnetic pole. The field intensity is also specified by number of lines of force intersecting unit area normal to the field, equal numerically to field strength in Oersted.

Magnetic Induction

When any substance is subjected to a magnetic field, the magnetic flux per unit area taken perpendicular to direction of the flux is called magnetic induction.

Magnetic Permeability

Property of materials modifying the action of magnetic poles placed there in and modifying the magnetic induction resulting when the material is subjected to a magnetic field or magnetizing force. The permeability may be defined as ratio of magnetic induction in the substance to magnetizing field to which it is subjected.

Magic Number

When the number of protons is 2,8,20,28,50,82 or the no. of neutrons is 2,8,20,28,50,82,126 the nucleus is observed particularly stable and these numbers are referred to as magic numbers. Nuclei in which the no. of protons as well as no. of neutrons is equal to magic number belong to most stable group of nuclei.

Magnetic Dipole

Small bar magnet composed of north and south poles.

Magnetic Flux Density

 Also called as magnetic induction represents magnitude of internal field strength with in a substance that is subjected to an external magnetic field.

Magnetic Moment

A vector quantity that is a measure of the torque exerted on a magnetic system when placed in magnetic field and that for a magnet is the product of distance between its poles and the strength of either pole. It is usually created by electric current flowing in wire or with orbital motion of spinning electron caused intrinsic magnetic moment.

Magnetic Potential

Magnetic potential at a point is measured by the work required to bring unit positive pole from an infinite distance (zero potential) to the point.

Magnetic Resonance Imaging (MRI)

The use of magnetic fields and radio waves (instead of the X-rays employed in the CT scan) to visualize body structures and how they function. The powerful magnet, large enough to enclose the body, forces the atomic nuclei in most material such as soft tissue to align themselves with the magnetic field. Radio waves are aimed at the selected area to excite the atoms which, when the waves are stopped, emit signals that are converted to computer-generated pictures.

Magnetic Susceptibility

 It is a dimension less quantity and is proportionality constant between magnetization & applied external magnetic field.   

Magnetism

Old study which deals with simplest sources of magnetic fields, the permanent (bar) magnets. Magnets and magnetic fields are dealt without considering electrical charges in motion.

 

Magnetization

The phenomenon of formation of magnetic dipoles inside material due to application of uniform magnetic field.

(or)

The total magnetic moment per unit volume of material is called as magnetization.   

Magnetoresistance

It is property of crystal to change its electrical resistance when a magnetic field is imposed on it.

Magnetometer

An instrument used for measuring the intensity or direction of a magnetic field, especially the earth’s magnetic field.

Magnetostriction

The phenomenon of change in shape and density of a substance, especially a ferromagnetic substance, when exposed to a magnetic field is called magnetostriction. 

Magnification

The apparent enlargement of an object by an optical instrument is called magnification.