Measures the acidity of a solution. It is the negative logarithm of the concentration of the hydrogen ions in a substance.
A vesicle which encloses material from coming from the outside of the cell by endocytosis .
The geological eon covering about 570 million years ago to present day.
A monostable pentode circuit used to generate sharp pulses at an adjustable and accurately timed interval after receipt of a triggering signal.
Phantom Power
The standardized scheme of providing power supply voltage to certain microphones using the same two lines as the balanced audio path.
Identification, isolation, and characterization of biologically active substances in living things.
The study of drugs, which includes determination of biological activity, biological effects, breakdown and synthesis, and delivery.
Phase identifies the position at any instant which a periodic wave occupies in its cycle. A portion of a material system whose properties and composition are homogeneous and which is physically distinct from other parts of the system.
Phase Angle
The number of electrical degrees of lead or lag between the voltage and current waveforms in an ac circuit.
Phase Boundary
A surface where two samples of matter with different properties are in contact.
Phase Change
The change from gas to liquid to solid.
Phase Delay
The time or angular difference between two signals.
Phase Diagram
Graphical representation of the temperature and composition limits of phase fields in an alloy or ceramic system.
Phase Locked Loop
An electronic circuit with a voltage- or current-driven oscillator that is constantly adjusted to match in phase the frequency of an input signal.
Phase Modulation
Angle modulation in which the phase of the carrier is controlled by the modulating waveform.
Phase Rule
This states that the maximum number of phases (P) that may coexist at equilibrium is two plus the number of components (C) in the mixture minus the number of degrees of freedom (F): P + F = C + 2.
Phase Separation
The phenomenon of a separation of a liquid or vapour into two or more physically distinct and mechanically separable portions or layers.
Phase Shift
The time or angular difference between two signals.
Phase Shifter
A device used to change the phase relationship between two ac signals.
Phase Transformation
Changes that can occur within a given material system.
Phase Velocity
The velocity with which planes of equal phase, crests or troughs, progress through the medium.
Phased Array Antenna
An array antenna whose beam direction or radiation pattern is controlled primarily by the relative phases of the excitation coefficients of the radiating elements.
Phased Array Radar
Radar using many antenna elements which are combined in a controlled phase relationship.
Also known as carbolic acid. It is used as a strong disinfectant.
Phenolic Resin
A condensation reaction polymer. A key characteristic of phenolic resin is the ability to withstand high temperature, along with mechanical load with minimal deformation or creep. In other words, cured phenolic resin provides the product rigidity necessary to maintain structural integrity and dimensional stability even under severe conditions.

The observable characteristics of an organism.
A molecular group or fragment formed by abstracting or substituting one of the hydrogen atoms attached to a benzene ring.
Phenyl Methyl Ketone
Alternative name for Acetophenone.
Alternative name for Aniline.
A letter of the Greek alphabet.
Philosopher′s Wool
An old name for Zinc Oxide.
Phlogisticated Air
An old name for Nitrogen.
A hypothetical elastic fluid which was seen as a metalizing and combustible principle.
The unit of measurement for loudness level.
The basic classes of sounds used to form the words of a language. Examples in English are "k", "oo", and "th". They are often represented by single written letters.
Phonetic Alphabet
Used when communicating over the radio to ensure there is no miscommunication of important information.
An instrument for measuring the intensity or frequency of sounds.
A single quantum of vibrational or elastic energy.
An ion, compound, or salt containing phosphorus and oxygen.
Phosphodiester Linkage
A chemical grouping that contains two alcohols esterified to one molecule of phosphoric acid.
A lipid containing one or more phosphate groups.
Phosphor Bronze
An alloy of copper with 3.5 to 10% of tin and a significant phosphorus content of up to 1%.

The property of a material whereby it continues to emit visible light after it has been illuminated by ultraviolet light.
Phosphoric Acid


An inorganic acid.

Phosphoric Acid Fuel Cell
Operates at temperatures around 150 to 200°C and use phosphoric acid as the electrolyte.
Cleavage of a compound with phosphate as the attacking group.
A non-metallic element.
Formation of a phosphate derivative of a biomolecule.
Photometric unit of illuminance or illumination equal to 1 lumen per square centimetre.
Photo Etching
Chemical process of removing unwanted material in producing printed circuit boards.
A light-controlled variable resistor which has a light-to-dark resistance ratio of 1:1000.
Photochemical Reaction Centre
The part of a photosynthetic complex where the energy of an absorbed photon causes charge separation, initiating electron transfer.
The study of the effects of light on chemical reactions.
A light-controlled PN junction. Current flow increases when the PN junction is exposed to an external light source.
Photoelectric Effect
The ejection of electrons from metallic surfaces by illuminating light.
Photoelectric Sensor
An electrical device that responds to a change in the intensity of the light falling upon it.
Photoelectric Voltage
A voltage produced by light.
Photoelectrochemical Cell
A type of photovoltaic device in which the electricity induced in the cell is used immediately within the cell to produce a chemical, such as hydrogen, which can then be withdrawn for use.
An electron ejected from an atom or molecule that has absorbed a photon.
The study of light.
Luminescence caused by absorption of optical radiation.
An instrument which measures luminous intensity.
Massless packet of energy, which behaves like both a wave and a particle.
The enzymatic formation of ATP from ADP coupled to the light-dependent transfer of electrons from water in photosynthetic cells.
The light-induced reduction of NADP in photosynthetic cells.
The layer of the Sun from which all visible light reaches us.
Process by which green plants convert light to energy by transforming carbon dioxide and water into carbohydrates.
A transistor with a window on the top face to allow light to fall on the active surface.
An organism that can use the energy of light to synthesize its own fuels from simple molecules such as carbon dioxide, oxygen, and water.
Photovoltaic Array
An interconnected system of PV modules that function as a single electricity-producing unit.
Photovoltaic Cell
A unit which generates a voltage related to the light intensity impinging on it.
Photovoltaic Cell Efficiency
Alternative name for Solar Cell Efficiency.
Photovoltaic System
The complete set of components for converting sunlight into electricity by the photovoltaic process, including the array, inverter and the balance of system components.
Phreatic Eruption
An explosive volcanic eruption caused when water and heated volcanic rocks interact to produce a violent expulsion of steam and pulverized rocks.
An explosive volcanic eruption that results from the interaction of surface or subsurface water and magma.
Physical Change
A change which does not transform one substance into another.
Physical Chemistry
A branch of chemistry that studies chemical phenomena from a physical and mathematical perspective.
Physical Constants
From Avogadro's number to the speed of light in vacuo.
Physical Property
Measurement of a physical property may change the arrangement but not the structure of the molecules of a material.
Lists all the Physics topics
Physics Books
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Physics Calculations
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Physiological Acceleration
The acceleration experienced by a human in an accelerating vehicle.
Materials extracted from plant tissue.
The study of substances found in plants.
The plant forms of plankton.