Po

Po
Pockels Cell
A Pockels Cell is a device which contains a photo refractive crystal. When a voltage is applied to this crystal it can change the polarisation or phase of the light beam.
pOH
Measures the basicity of a solution. It is the negative logarithm of the concentration of the hydroxide ions.
Point
A zero-dimensional figure.
Point Contact Diode
A diode in which the end of a fine wire is pressed against a semiconductor.
Point Defect
A crystalline defect associated with one or, at most, several atomic sites.
Point Mobility
The velocity at a point per unit force at the same point and same direction.
Point Source
Ideally, a source with infinitesimal dimensions.
Point to Point Wiring
Individual wires run from terminal to terminal to complete a circuit.
Point Type Face
Unit of measurement for type faces.
Pointer
A register that holds an address of data rather than the data.
Poise
Named after the physicist Poiseuille this is the CGS derived unit of dynamic viscosity.
Poiseuilles Equation
Gives the volume flow rate of an incompressible fluid in a round pipe.
Poisson Constant
The ratio of the gas constant to the specific heat of a gas at constant pressure.
Poisson Distribution
A distribution often used to express probabilities concerning the number of events per unit.
Poisson Equation
A fundamental equation of mathematical physics, describing the spatial variation of a potential function for given source terms.
Poisson Spot
Poisson originally predicted the existence of the arago spot, and used the prediction to demonstrate how the wave theory of light must be in error to produce such a counterintuitive result.
Poissons Ratio
Ratio of strain in the lateral direction to strain in the axial direction.
Polar Axis
In the polar coordinate system, a ray from the pole in a fixed direction, analogous to the x-axis in the Cartesian system.
Polar Bond
A bond involving electrons that are unequally shared.
Polar Coordinates
The position of a point is defined as the distance from the origin and an angle relative to the x axis.
Polar Form of Complex Numbers
Complex numbers written in polar form.
Polar Molecules
Molecule with a partial charge.
Polar Moment of Inertia
The resulting inertia of mass forward and rearward of the centre of gravity.
Polar Orbiting Satellite
An artificial satellite that has an orbit that travels over the vicinity of the geographic poles.
Polarimeter
An instrument for determining the degree of polarization of electromagnetic radiation.
Polarisation Curve
A measure of cell performance that indicates the relationship between current density and voltage across a fuel cell.
Polariscope
An instrument for detecting polarized radiation and investigating its properties.
Polariser
A polariser is a device which absorbs all the components of an electro-magnetic field in one direction leaving only the components perpendicular to that of polariser axis.
Polarity
The positive or negative direction of an electrical, acoustical or magnetic force.
Polarization
For an atom, the displacement of the centre of the negatively charged electron cloud relative to the positive nucleus, which is induced by an electric field.
Polarized
A property of a transverse wave when its vibrations are all in a single plane.
Pole
An old English unit of length or the coldest regions on a planet.
Pole Piece
The shaped magnetic material upon which the stator windings of motors and generators are mounted or wound.
Pole Strength
The concept of an isolated magnetic pole (magnetic monopole) has been abandoned. However, it is used as a concept in magnetometry. Pole strength is defined as that which when placed in a unit induction experiences a force of 1 newton.
Polonium
Polyamide
A macromolecule with repeating units linked by amide bonds.
Polyatomic Ion
An ion formed by the loss or gain of electrons from a molecule or chemical group composed of two or more atoms.
Polyatomic Molecule
An uncharged particle that contains more than two atoms.
Polycarbonate
A thermoplastic that can be shaped and formed through a number of manufacturing processes. It machines well and can be solvent bonded and welded. It is tough and resistant to damage which is an ideal property for a mobile phone. If dropped, a mobile phone with a polycarbonate casing is likely to survive undamaged. It is an insulator, often used to insulate electrical circuits. Supplied in a range of colours.

Polycrystalline
Referring to crystalline materials that are composed of more than one crystal or grain.
Polycrystalline Solar Cell
Cheap to make as the conditions required to produce the silicon wafers do not need to be so tightly controlled.
Polydentate Ligand
A ligand that has more than one atom that coordinates directly to the central atom in a complex.
Polyethylene
Plastic used heavily in the packaging industry.

Polygon
A shape of multiple sides. Regular polygons have sides of equal length.
Polyhedral
In the shape of a solid formed by plane faces, as in a prism.
Polyimide
a polymer of imide monomers.
Polymer
A large molecule formed by the linking together of many smaller molecules known as monomers.
Polymer Matrix Composite
A composite that uses a polymer as the matrix phase.
Polymeric Dispersant
A water-soluble polymer that acts as a suspending agent promoting the suspension of particles in water so that they resist settling.
Polymerization
The process by which monomers are joined together to give a polymer.
Polymerize
To link smaller molecules together to form a larger molecule.
Polymethyl Methacrylate Resin
Commonly known as perspex or lucite, a transparent plastic.

Polymorphism
Different crystal structures at different temperatures or pressures for a single compound.
Polynomial
A function that is a sum of power functions, with positive integer exponents, multiplied by constants.
Polynuclear Aromatic Hydrocarbons
Aromatic hydrocarbons with two or more (up to five or six) benzene rings joined in various, more or less clustered forms.
Polyomino
A planar figure consisting of congruent squares joined edge-to-edge.
Polyphase AC
An electrical current which is generated in two or more phases each having exactly the same the same frequency.
Polyphosphate
A chemical compound formed by the adjoining of phosphate ions.
Polysaccharide
A carbohydrate consisting of a large number of linked monosaccharide units.
Polystyrene
Expanded polystyrene was the first foamed polymer. It is the white rigid plastic used for thermal insulation and in flotation devices.

Polytetrafluoroethylene
Commonly known as Teflon, a thermoplastic polymer used for non-stick coatings and bearings.

Polythene
Alternative name for Polyethylene.
Polytropic Process
A non-adiabatic reversible process characterized by the equation of path, pv = constant.
Polyurethane
Polymer composed of a chain of organic units joined by carbamate links.

Polyvinyl Acetate
A colorless, thermoplastic, water soluble, resinous high polymer derived from the polymerization of vinyl acetate with a catalyst. Abbreviated as PVA.

Polyvinyl Alcohol

(C2H4)n

Odorless and nontoxic with excellent film forming, emulsifying, and adhesive properties with resistance to oil, grease and solvent.

Polyvinyl Chloride
Plastic used in many different forms. Commonly abbreviated as PVC.

Polyvinylpyrrolidone
Soluble in water and other polar solvents. Used as a coating or an additive in coatings.

Ponderous Spar
Old name for Barium Sulphate.
Pop
An undesirable short duration microphone output, often caused by explosive exhalation of air during the formation of certain vocal sounds.
Pop Valve
A spring loaded safety valve that opens automatically when pressure exceeds the limits for which the valve is set.
POP3
Abbreviation of Post Office Protocol version 3.
Poplar
A light wood, but not very strong and or very good wear resistance.
Poppet Valve
A valve opened by the action of a cam and closed by a spring.
Population
The total number of unique values.
Porcelain
Made from china clay, a clay consisting mainly of kaolinite.
Pore Size Distribution
The ratio of the number of effective holes of a given size to the total number of effective holes per unit area expressed as a percent and as a function of hole size.
Porosity
The presence of gas pockets within a solid material.
Porous Bearing
Made from porous material, such as compressed metal powders, the pores acting either as reservoirs for holding or passages for supplied lubricant.
Port
An opening hole, or passage.
Portals, News and Directories
Lists all Portals News and Directories topics in the Encyclopaedia
Lists all Portals News and Directories Weblinks in the Encyclopaedia
Portico
A structure usually attached to a building, such as a porch, consisting of a roof supported by piers or columns.
Position Sensor
A component in a servosystem that measures position and converts the measurement into a form convenient for transmission as a feedback signal.
Position Servosystem
A servosystem whose end function is to control the position of the load it is driving.
Positional Notation
A numbering system in which a number is represented by means of a stated set of symbols or digits, such that the value contributed by each symbol or digit depends upon its position as well as upon its value.
Positional Weighting
The value given a digit based on the digit′s position within a given number.
Positive
A quantity or value that is greater than zero.
Positive Alternation
The part of a sine wave that is above the reference line.
Positive Charge
The electrical potential acquired by an atom which has lost one or more electrons; a characteristic of a cation.
Positive Clamper
A circuit that clamps the lower extremity of the output waveshape to a dc potential of 0 volts.
Positive Displacement Pump
A pump that moves a measured quantity of fluid with each stroke of a piston or each revolution of vanes or gears.
Positive Feedback
Feedback in which the feedback signal is in phase with the input signal.
Positive Logic
The form of logic in which the more positive logic level represents 1 and the more negative level represents 0.
Positive Number
A number larger than 0.
Positive Temperature Coefficient
The characteristic of a conductor in which the resistance increases as temperature increases.
Positron
The antiparticle of the electron.
Post Office Protocol version 3
A protocol for transmitting and receiving email.
Post Triggering
The technique used on a DAQ board to acquire a programmed number of samples after trigger conditions are met.
Postcure
An additional elevated temperature exposure that is performed often without tooling or pressure to improve elevated temperature mechanical properties.
Postulate
A statement assumed to be true without proof.
Pot Life
The length of time a catalyzed thermosetting resin system retains a viscosity low enough for it to be suitable for processing.
Potable Water
Another name for drinking water.
Potash
Old fashioned name for Potassium Carbonate made from the ashes of burnt wood.
Potassium
A soft, silvery coloured metal, which like other members of the alkali group of metals, is extremely reactive.
Potassium Acetate

KC2H3O2

The potassium salt of acetic acid, used as a deicer instead of chloride salts such as calcium chloride or magnesium chloride.

Potassium Bromide

KBr

A white crystalline salt used in photography. It was used in medicine as a sedative.

Potassium Carbonate

K2CO3

A white very soluble deliquescent salt.

Potassium Chloride

KCl

White crystalline solid.

Potassium Fluoride

KF

White crystalline solid.

Potassium Hydroxide

KOH

A white deliquescent solid that dissolves in water to give an alkaline solution.

Potassium Iodide

KI

White crystalline solid.

Potassium Manganate VII

KMnO4

Deep purple, crystalline, soluble salt. Dissolves in water to produce a strong oxidizing agent. Used as a disinfectant.

Potassium Nitrate

KNO3

The salt of potassium and nitric acid. Used in pyrotechnics, explosives, the manufacture of glass and as a fertilizer.

Potassium Oxide

K2O

Yellowish white yo grey crystalline solid.

Potassium Permanganate
Deep purple, crystalline, soluble salt.
Potassium Peroxide

K2O2

Yellow or orange solid.

Potassium Sulphide

K2S

White, yellow, red or brown.

Potassium Superoxide

KO2

Yellow crystalline solid.

Potential Barrier
The internal resistance of a transistor related to the internal potential existing between NP junctions.
Potential Difference
The difference of potential produced by an electrical source to drive a current through an external electrical circuit.
Potential Energy
The energy a body possesses due to it's position or the arrangement of it's parts.
The local space rate of change of any potential.
Potential Transformer
The voltage supplied to a primary coil induces a voltage in a secondary coil according, to the ratio of the wire windings in each of the coils.
Potentiometer
A variable resistor with three terminals-one on each end of the resistor and one "wiper" which contacts the resistor midpoint to indicate a variable position.
Potin
An ancient alloy of copper, zinc, lead and tin that was used to make coins.

Potting Compound
An insulating material for encapsulating one or more circuit elements.
Pouch Cell Battery
A soft case battery cell.
Poultice Corrosion
Corrosion occurring under or around a deposit on a metallic surface.
Pound
The unit of mass in the British system of units.
Pound Force
pound-force (lbf) = 4.44822 N
Pound Force Foot
The unit of torque in the old British system of units, abbreviated lbf ft.
Pound per Cubic Foot
Pound per Cubic Inch
Poundal
A derived unit of force in the British system of units.
Pounds per Square Inch
A British imperial unit of pressure. 1.0 psi = 6894.757 Pa
Pour Point
Low-temperature flow indicator and is 3°C above the temperature to which a normally liquid petroleum product maintains fluidity.
Pour Point Depressant
An additive which retards the adverse effects of wax crystallization, and lowers the pour point.
Pour Stability
The ability of a pour depressed oil to maintain its original pour point when subjected to long-term storage at low temperature approximating winter conditions.
Powdered Baking Ammonia
Alternative name for Ammonium Bicarbonate.
Power
Power is defined as the rate of doing work.
Power Amplifier
An amplifier in which the output-signal power is greater than the input-signal power.
Power Curve
Graphical representation of the changing relationship between speed and revolutions per minute (RPM).
Power Density
Characteristic parameter of a battery/electrical power source indicating its electrical power per unit weight or volume.
Power Factor
The cosine of the phase angle between voltage and current.
Power Flux Density
In radio wave propagation, the power crossing unit area normal to the direction of wave propagation.
Power Gain
In an antenna, the ratio of its radiated power to that of a reference.
Power Hacksaw
Machine fitted with serrated blade held taut in a reciprocating frame that cuts in one direction, either on the forward or return stroke.
Power Loss
The electrical power, supplied to a circuit, that does no work and is usually dissipated as heat.
Power Lost to Engine Friction
This can be calculated from the difference between Indicated Power and Brake Power.
Power of a Lens
The power of a lens is defined as the reciprocal of its focal length, in metres.
Power Pentode
A special purpose tube used to provide high-current gain or power amplification.
Power Spectral Density
A method of scaling the amplitude axis of spectra of random rather than deterministic signals.
Power Standing Wave Ratio
The ratio of the square of the maximum and minimum values of a wave.
Power Stroke
The working stroke of a piston.
Power Supply
A unit that supplies electrical power to another unit.
Power Surface Density
Radiant power incident on a small sphere, divided by the cross-sectional area of that sphere.
Power to Weight Ratio
The power produced by a machine divided by the weight of the machine.
Powerline Carrier System
A method of sending information over an electrical power distribution system.
Power-Split Hybrid Vehicle
The power may be provided by the internal combustion engine or the electric motor or a combination of the two.
Poynting-Robertson Effect
Gradual decrease in orbital velocity of a small particle in orbit about the sun due to the absorption and reemission of radiant energy by the particle.