Farad

the unit in which CAPACITANCE is measured. It is usually denoted by the symbol F. For example, the capacitance (C) of a conductor measured in farads is the charge (in coulombs) needed to raise the potential by one volt i.e. 1 farad = 1 coulomb per volt (1F = 1 CV^-1). As the farad itself is usually too large a quantity for most applications, the practical unit is the microfarad (µF), or one millionth of a farad.

Taken from Dictionary of Science

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The farad (symbol: F) is the SI unit of capacitance. The term farad is named after the English physicist Michael Faraday.

A farad is the charge in coulombs a capacitor will accept for the potential across it to change 1 volt. A coulomb is 1 ampere second. Example: A 47 mA current causes the voltage across a capacitor to increase 1 volt per second. It therefore has a capacitance of 47 mF. It has the base SI representation of s⁴·A²·m^-2·kg^-1. Further equalities follow:

The most commonly used multiples and submultiples in electrical and electronic usage are the microfarad, nanofarad and picofarad.

Taken from Wikipedia

Valency

is the bonding potential or combining power of an atom or group, measured by the number of hydrogen ions (H⁺, or equivalent) that the atoms could combine with or replace. In an ionic compound, the charge on each ion represents the valency, e.g., in NaCl, both Na⁺ and Cl^- have a valency of one. In covalent compounds, the valency is represented by the number of bonds formed. In carbon dioxide, CO₂, carbon has a valency of 4 and oxygen 2.

The electronic theory of valency explains bonds through the assumption that specific arrangements of outer electrons in atoms (outer shells of eight electrons) give stability (as with the inert gases, which have such a structure) through the transfer or sharing of electrons. Thus with the combination of sodium with chlorine, sodium has one electron in the outer shell, which it loses to chlorine to form the stable structure of the inert gas neon. Similarly, the gain of one electron by chlorine gives it the stable structure of argon.

Taken from Dictionary of Science

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In chemistry, valence, also known as valency or valency number, is a measure of the number of chemical bonds formed by the atoms of a given element. Over the last century, the concept of valence evolved into a range of approaches for describing the chemical bond, including Lewis structures (1916), valence bond theory (1927), molecular orbitals (1928), valence shell electron pair repulsion theory (1958) and all the advanced methods of quantum chemistry.

Taken from Wikipedia

Absolute Temperature

a temperature measured on the KELVIN SCALE with respect to ABSOLUTE ZERO.

Taken from Dictionary of Science

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Absolute, or thermodynamic, temperature is conventionally measured in kelvins (Celsius-scaled increments) and in the Rankine scale (Fahrenheit-scaled increments) with increasing rarity. Absolute temperature measurement is uniquely determined by a multiplicative constant which specifies the size of the "degree", so the ratios of two absolute temperatures, T₂/T₁, are the same in all scales. The most transparent definition of this standard comes from the Maxwell-Boltzmann distribution. It can also be found in Fermi-Dirac statistics (for particles of half-integer spin) and Bose-Einstein statistics (for particles of integer spin). All of these define the relative numbers of particles in a system as decreasing exponential functions of energy (at the particle level) over kT, with k representing the Boltzmann constant and T representing the temperature observed at the macroscopic level.

Taken from Wikipedia

Background

'interference' which affects the reading of a signal that is being measured. The interference signals come from sources such as natural RADIOACTIVITY and COSMIC RAYS and must be allowed for when measurements are being taken.

Taken from Dictionary of Science