P
 Pyrometer: Device used for measuring very high temperatures based on principle of radiation. Proton: Sub atomic particle having positive charge of one electron unit and constituent of nucleus. Positron: Anti particle for electron having same mass as electron but with positive charge of same magnitude. 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. Photo conductor: It is an optoelectronic device that absorbs optical energy and converts into electrical energy. The operation of device is based on increase of conductivity of a specific region with photo excitation. The photo generated electrons and holes are collected by opposite contacts and result in a photo current. 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. Poynting vector: It is the energy per unit area per unit time transported by electromagnetic field. Polarization (EM wave): The property of acquiring one sidedness by a wave is known as polarization. The wave unsymmetrical about a direction is called polarized wave while that symmetrical is called as unpolarized wave. The polarization is the phenomenon which shows that electromagnetic waves are transverse in nature. Polarisation: It is defined as total induced dipole moment per unit volume. (or) The phenomenon of formation of dipoles when a uniform electric field is applied on a non uniform dielectric is called polarisation. Parking orbit: The orbit in which a geo-stationary satellite moves is called parking orbit. 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. Prism: It is a homogenous, transparent medium (such as glass) enclosed by two refracting plane surfaces at an angle. Photo detector: An optoelectronic device that absorbs optical energy and converts it into electrical energy, which usually manifests as photo current is called as photo detector. Penetration depth: It is the depth from surface of metal at which magnetic field falls to 1/e of its original value. Polymorphism: The property exhibited by some crystals according to which they exist at different crystal structures at different temperatures. Phase (SHM): Fraction of time interval that has elapsed since the particle crossed the mean position of rest in the positive direction. (or) It is the ratio of displacement of vibrating particle at any instant to the amplitude of vibrating particle. Plastic deformation: It is deformed state of a substance where the stress is no longer proportional to strain and permanently non recoverable. From atomic perspective, plastic deformation corresponds to breaking of bonds with original atom neighbors and then reforming bonds with new neighbors as large no. of atoms move relative to each other. Pickling: Process of chemical removal of oxides and other surface layers, leaving the cleaned part with a metallic appearance. 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.Pascal’s principle: Pressure applied to an enclosed fluid is transmitted to every portion of fluid and to walls of containing vessel. 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.Photon:Term attributed to particle nature of light. Photo Conductor: Optoelectronic device that absorbs optical energy and converts into electrical energy. The operation of device is based on increase of conductivity of a specific region with photo excitation. The photo generated electrons and holes are collected by opposite contacts and result in a photo current. Polarization: The property of acquiring one sidedness by a wave is known as “Polarization”. The wave unsymmetrical about a direction is called polarized wave while that symmetrical is called unpolarized wave. The “Polarization” is phenomenon which shows that electromagnetic waves are transverse in nature. 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 flow out through the surface.    Poynting’s Vector: It is the energy per unit area, per unit time, transported by electromagnetic field. Pyrometer: Device used for measuring very high temperatures based on principle of radiation. Periodic table: Table used to classify all the elements according to electron configuration. The elements are arranged in table with increasing atomic number in horizontal rows. The arrangement is such that all elements arrayed in a column or group has similar valence electron structures as well as chemical and physical properties. These properties change gradually and symmetrically, moving horizontally across each period.     Poly-crystal: It is a substance in which crystal structure is a collection of many small crystals or grains. Phase: A homogeneous portion of a system that has uniform physical and chemical characteristics. Polarization (ionic): Displacement of anions & cations in opposite direction. Powder metallurgy: The fabrication of metal pieces having intricate and precise shapes by the compaction of metal powders, followed by densification heat treatment. Precipitation hardening: Hardening and strengthening of a metal alloy by extremely small and uniformly dispersed particles that precipitate from a supersaturated solid solution. P- type semiconductor: A semiconductor which is doped with acceptor impurity atoms leading to holes as predominant charge carriers responsible for electrical conduction. Polar molecule: A molecule in which there exists a permanent electric dipole moment by virtue of the asymmetrical distribution of positively and negatively charged regions. 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 0oC on increasing (or decreasing) its temperature by 1oC. Prevost’s theory of heat exchange: Each body emits thermal radiations at all temperatures, but for absolute zero and it absorbs radiations emitted from all other bodies in its surroundings. Principle of equal apriori probabiltiy: According to the postulate, 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. Perpendicular Axes Theorem: Sum of the moments of inertia of a uniform plane lamina about any two perpendicular axes in its plane is equal to the moment of inertia of it about an axis perpendicular to its plane which passes through the point of intersection of first two axes. Parallel Axes Theorem: The moment of inertia of a body about any axis is equal to sum of the moment of inertia of the same body about an axis parallel to the first axis which passes through the center of gravity and product of mass of the body and square of the perpendicular distance between the axes. Parking orbit: The orbit in which a geo-stationary satellite moves is called as parking orbit. Periodic motion: Any motion that repeats itself at regular intervals of time is known as periodic motion. Phase constant: It is the initial phase of the particle in SHM. Plasticity: The property of a body by virtue of which it cannot regain its original shape or size after removal of deforming forces. Principle of invariance of charge: According to this principle, the total charge in an isolated system is unchanged by motion of its charge carriers. (Or) The total electric charge of an isolated system is relativistically invariant. Photoelectric effect: This absorption process refers to an interaction of the incident photon of energy greater than binding energy of a bound electron of absorber atom as a result of which entire photon energy is absorbed and electron is ejected.  Pair production: When the incident photon energy exceeds twice the rest mass energy of an electron, this interaction is more probable. In this interaction, known as pair production, the incident photon is completely absorbed, and in its place appears an electron-positron pair.  Phase point: The instantaneous state of a particle in phase space is represented by a point known as phase point. Phase space: In Heisenberg’s point of view, the state of a single particle is determined by position coordinates x, y, z and momentum coordinates Px, Py, Pz totally comprising six dimensions. This space is called as phase space. Pseudo Vector: Any vector which commutes with parity operator is a pseudo vector.