PHYSICS DICTIONARY

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Power

The rate at which work is done, or energy expended, per unit time.

Poynting Vector

 It is the energy per unit area per unit time transported by electromagnetic field.

Poynting’s Theorem

According to the theorem, the work done on charges by electromagnetic field is equal to decrease in energy stored in field less the energy that flowed out through the surface.

Precession of Equinoxes

The precessional motion of earth’s axis causes a change in direction of line of equinoxes which is called precession of equinoxes.

Precipitation Hardening

 Hardening and strengthening of a metal alloy by extremely small and uniformly dispersed particles that precipitate from a supersaturated solid solution is called as precipitation hardening.

Pressure Law

At constant volume, the pressure of a given mass of a gas increases (or decreases) by (1/273)th of its pressure at 0 oC on increasing (or decreasing) its temperature by 1oC.

Pressure Transducer

 It is an electronic device that converts pressure into electrical signals that can be recorded digitally.

Pressure

 Pressure on any surface is defined as normal force per unit area of surface.

Prevost’s Theory of Heat Exchange

 Each body emits thermal radiation at all temperatures, but for absolute zero; and it absorbs radiations emitted from all other bodies in its surroundings.

Primary Bonds

Inter atomic bonds that are relatively strong and for which bonding energies are relatively large. Primary bonding types are ionic, covalent, and metallic.

Primary Colors

Almost all visible colors can be obtained by the additive color mixing of three colors that are in widely spaced regions of the visible spectrum. If the three colors of light can be mixed to produce white, they are called primary colors and the standard additive primary colors are red, green and blue.

Principal Points

 The principal points are a pair of conjugate points on the principal axis for which linear magnification is unity and positive.

Principle of Calorimeter

If no heat is lost to surroundings, the heat lost by hot body must be equal to heat gained by cold body.

Principle of Calorimetry

 When hot body and cold body are joined together, they attain common temperature and heat lost by hot body is equal to heat gained by cold body provided there is no loss of heat to surroundings by conduction, convection or radiation.

Principle of Degradation of Energy

 All the available energy of universe is tending towards zero i.e., entropy is reaching its maximum value.

Principle of Equal Apriori Probability

According to this principle, the probability of finding the phase point for given system in any region of phase space is identical with that for any other region of equal extension or volume.

Principle of Equivalence

In the neighborhood of any given point it is not possible to distinguish between the gravitational field produced by the attraction of masses and the field produced by accelerating a inertial frame of reference.

Principle of Homogeneity of Dimensions

The principle states that physical quantities of same dimensions only can be added or subtracted or equated.

Principle of Invariance of Charge

 According to this principle, the total charge in an isolated system is unchanged by motion of its charge carriers.

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 The total electric charge of an isolated system is relativistically invariant.

Principle of Least Time

Same as Fermat’s principle of extremum path.

Principle of Regenerative Cooling

Regenerative cooling is a method of cooling gases in which compressed gas is cooled by allowing it to expand and thereby taking heat from the surroundings, the cooled expanded gas then passes through a heat exchanger where it cools the incoming compressed gas.

Principle of Reversibility

If all velocities in a dynamical system are reversed, the whole previous motion has to be obtained provided there is no dissipation.

Principle Quantum Number

It is one of four quantum numbers associated with energy levels in an atom. The principle quantum number has integer values    1, 2, 3……. corresponding to order of orbit containing electrons.

Prism

It is a homogenous, transparent medium (such as glass) enclosed by two refracting plane surfaces at an angle.

Probability Density Function

The outcome of a repeatable experiment, usually referred to as a random variable, is not always discrete and usually can take any value within a continuous range. If ‘x’ is continuous then the probability that the outcome lies between x and x+dx can be written as P(x)=f(x;θ)dx. Here f(x, θ) is called the probability density function.

Process

A process is the path along which a change of state takes place. The process can occur under variety of conditions which must be defined because many things depend on nature of process. For a substance, isothermal, isochoric, adiabatic, cyclic etc are examples of process.

Progressive Wave Motion

Wave motion in which there is no transfer of medium in direction of propagation wave, but there is always transfer of energy in the direction of propagation of wave.

Progressive Wave

If we produce waves continuously in a medium, at any instant, all the particles of medium start vibrating in same manner, but different particles are in different states of their vibrations. The disturbance or wave so produced in the medium is called progressive wave.

Projectile

A body projected with certain velocity making an angle other than 90o to the horizontal is known as projectile.


Prompt Neutron

Neutrons released in fission within 10-14 sec or less. 

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