PHYSICS DICTIONARY

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Perpetual Machine of First Kind

The perpetual machine is a hypothetical concept which provides mechanical work more than the heat absorbed by it. Perpetual machine will continue forever without external energy.

Perpetual Machine of Second Kind

It is an imaginary concept as per which,  a machine which can absorb heat from source and completely convert it into work without converting it into internal energy.

Perturbation Theory

A set of mathematical methods for obtaining approximate solutions to complex equations for which no exact solution is possible or known, generally involving an iterative algorithm in which each new term contributing to the solution has less significance than the last. In quantum physics, Feynman diagrams are used to calculate the terms for the perturbation theory solution of interactions between particles.

Peta

Prefix in metric system denoting 10¹⁵ of physical quantity

Pfund Series

The spectrum of wavelengths formed due to electronic transitions from higher states to fifth orbit of atom. The wavelengths fall in far infrared region. 

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.

Phase Constant

 It is the initial phase of the particle in SHM.

Phase Plate

Device used to produce phase difference or path difference in ordinary and extra ordinary waves produced by plane polarized light.

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.

Phase Velocity

The phase velocity of a wave is the rate at which the phase of wave propagates in space. This is velocity at which phase of any one frequency component of wave travels. For such a component, any given phase of wave will appear to travel at phase velocity.

or

When a progressive wave of a definite wavelength propagates in a medium, the velocity of propagation of its wave front is called phase velocity or wave velocity.

Phase (Wave Motion)

Ratio of displacement of vibrating particle at any instant to the amplitude of vibrating particle

or

It is defined as fraction of time interval that has elapsed since the particle crossed the mean position of rest in the possible direction.

Phase

A homogeneous portion of a system that has uniform physical and chemical characteristics is called as phase.

or

It is a Greek word “appearance” and is defined as a physically distinct but homogeneous part of a system which is separated from other parts of the system by finite bounding surface. Thus, each different, physically homogeneous part of a system is called as phase. For instance in water system consisting ice, water and its vapor, ice is the solid phase, water is liquid phase and vapor is gaseous phase.

Phon

A unit of apparent loudness, equal in number to the intensity in decibels of 1000 Hertz have perceived to be as loud as sound being measured.

Phonon

Hypothetical particle introduced for defining quantum of vibrational energy associated with atoms in crystal lattice.

Phosphorescence

Type of luminescence in which emission of light occurs with removal of excitation source with decay time of few seconds to hours or days.

Phot

A phot is a unit of illuminance, or luminous flux through an area. It is given as one lumen per cm².

Photo Conductivity

 Electrical conductivity that results from photon induced electron excitations in which light is absorbed. The phenomenon which is usually observed in photo conductors and other semi conductor devices.

PHYSICS DICTIONARY

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Paschen Series

The spectrum of wavelengths formed due to electronic transitions from higher energy states to third orbit of atom. The spectrum falls in infrared region.

Passive Component

 A passive device is one that contributes no power gain (amplification) to a circuit or system. It has no control action and doesn’t require any input than a signal to perform its function. In other words, they are components with no brains. Resistors, Capacitors, Inductors, etc fall under this class of components.

Pauli’s Exclusion Principle

The principle is postulated by an Austrian physicist Wolfgang Pauli in 1925. Pauli’s exclusion principle says that two similar particles cannot exist in same state, i.e. they cannot have both   position and velocity same within the limits given by uncertainty principle. The exclusion principle is crucial because it explains why matter particles do not collapse to a state of light density under influence of forces produced by particles of spin-0, 1& 2. If matter particles have nearly same positions, they must have different velocities, which mean that they will not stay in same position for long.

Peak Inverse Voltage

 It is maximum reverse voltage that a diode can with stand without destroying the junction.

Peltier Effect

When an electric current is passed through a junction of two dissimilar conductors , heat is either absorbed or released at the junction , depending on direction of current.

Penetration Depth

 It is the depth from surface of metal at which magnetic field falls to 1/e of its original value.

Penning Effect

Mechanism of adding small quantities of other gas having lower ionization potential into main gas, to reduce overall work function of gas composition is called Penning effect. If the main gas atoms having meta-stable excited states collide with additive gas atoms, then energy is transferred to additive gas by ionizing its atoms. In this fashion more charge is produced per unit energy of incident energy.

Penumbra

 (“from the Latin words Paene which means “nearly” and Umbra means “shadow” ) is the region in which only a portion of the light source is obscured by occluding body.  

                                        or     

Penumbra is the region where some or the entire light source is obscured. 

 

Perihelion

 It is the point in the orbit of a planet, where it is nearest to the sun.

Perigee

The point in the orbit of an object orbiting the earth, nearest to center of earth is called as Perigee. At its perigee, the objects travels faster than at any point in the orbit.

Periodic Motion

 Any motion that repeats itself at regular intervals of time is known as periodic motion.

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.   

Periscope

An arrangement of number of optical instruments like mirrors, lenses that enable user to view objects that are not in direct line of vision, such as one in a submarine for looking above surface of water.

Permanent Magnets

 They are materials which retains property of magnetism unless heated to a high temperature. They are made of hard steel or special alloys.

Permanent Set

 If wire is loaded beyond elastic limit, it will not regain its original length even after deforming force is removed. When the external load is completely removed, length of wire increased permanently called permanent set.

Permeance

The reciprocal of reluctance is called as Permeance.

Permeation

 Passage of a gas into, through, and out of a solid barrier; having no holes large enough to permit more than a small fraction of gas to pass through any hole, is known as permeation.

Permittivity

 It is the characteristic of dielectric material which determines that how much the electric field influences the material.

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.