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Physics Definitions

Primary Cell : A cell in which chemical action is not reversible is called a primary cell. e.g. Voltaic Cell, Daniel Cell, Leclanche Cell and dry Cell.
Permanent Magnets : Hardened steel and certain magnetic alloys (e.g. cobalt steel, tungsten steel etc.) when magnetized retain their magnetism indefinitely. Magnets made from such materials are called permanent magnets.
Plane Wavefront : At a large distance from a source of any kind, the wavefront will appear plane, Such a wavefront is called plane wavefront.
Polarization : The phenomenon of restricting the vibrations of a transverse wave in a particular direction is called polarization of transverse wave.
Polarization of Light : The phenomenon of restricting the vibrations of light in a particular plane is called polarization of light.
Photons : Radiation from a source is transmitted by tiny particles called photons.
Packing Fraction : The divergence of the nuclear mass from the nearest whole number (i.e. its mass number A) per nucleon is called packing fraction i.e. packing Fraction, f = M - A / A where M = actual mass of nucleus, A = mass number, As M - A is the mass defect, packing fraction may also be expressed as f = ΔM / A = mass defect/ mass number.
Primitives : The three sides a, b and c of the unit cell are known as primitives or characteristic intercepts.
Polycrystal : A crystal solid which is made up of a large number of monocrystals whose developed faces are joined together is called polycrystal.
p-Type Semiconductor : When a small amount of trivalent impurity is added to a pure semiconductor, it is called p-type semiconductor.
pn Junction : When a semiconductor crystal (germanium or silicon) is so prepared that one half is p-type and the other n-type, the contact surface dividing the two halves is called a pn junction.
Planet : A planet is heavenly body that the orbits the sun or another star and shines only by the light that it reflects.