Glossary of Physics (P)

 
Pascal: A unit of pressure, equal to the pressure resulting from a force of 1 Newton acting uniformly over an area of 1m2.
Pascal's law: The pressure exerted on a liquid is transmitted equally in all directions.
Paschen series: A group of lines in the infrared region in the spectrum of hydrogen.
Pauli Exclusion Principle: No two electrons in an atom can have the same four quantum numbers; thus, a maximum of two electrons can occupy a given orbital.
Peltier effect: The evolution or absorption of heat at the junction of two dissimilar metals carrying current.
Period of oscillation: The time required for one complete oscillation.
Periodic motion: The motion which repeats itself after regular intervals of time.
Photoelectric effect: The emission of electrons in some materials when light of suitable frequency falls on them.
Photons: A quanta of energy in light wave; the particle associated with light.
Planck's constant: The ratio of energy to frequency, equal to 6.63 x 10-34 joule-sec.
Plasma: A highly ionized gas composed entirely of equal number of positive ions and electrons.
Plasticity: The property of a solid whereby it undergoes a permanent change in shape or size when subjected to a stress.
Polarized Light: Light whose constituent transverse waves are all vibrating in the same plane.
Polaroid or polarizer: A device that produces polarized light.
Positron: An elementary particle having same mass as that of an electron but equal and positive charge.
Potential Energy: The energy possessed by a body by virtue of its position or configuration.
Power: The rate of doing work.
Pressure: The force per unit area.
Primary colors: Three colors red, yellow and blue, which can be combined in various proportions to produce any other color.
Principle quantum number: A quantum number that describes the main energy level of an electron in terms of its most probable distance from the nucleus.
Progressive wave: A wave which transfers energy from one part of a medium to another.
Projectile: An object which after being given an initial velocity is allowed to fall under the effect of gravity alone.