Units and Measurement
Category : UPSC
Units and Measurement
(i). Physics is a quantitative science, based on measurement of physical quantities. Certain physical quantities have been chosen as fundamental or base quantities (such as length, mass, time, electric current, thermodynamic temperature, amount of substance, and luminous intensity).
(ii). Each base quantity is defined in terms of a certain basic, arbitrarily chosen but properly standardized reference standard called unit (such as meter, kilogram, second, ampere, kelvin, mole and candela). The units for the fundamental or base quantities are called fundamental or base units.
(iii). Other physical quantities, derived from the base quantities, can be expressed as a combination of the base units and are called derived units. A complete set of units, both fundamental and derived, is called a system of units.
(iv). The International System of Units (SI) based on seven base units is at present internationally accepted unit system and is widely used throughout the world. The SI units are used in all physical measurements, for both the base quantities and the derived quantities obtained from them. Certain derived units are expressed by means of SI units with special names (such as joule, newton, watt, etc).
(v). The SI units have well defined and internationally accepted unit symbols (such as m for meter, kg for kilogram, s for second, A for ampere, N for newton etc.). Physical measurements are usually expressed for small and large quantities in scientific notation, with powers of 10. Scientific notation and the prefixes are used to simplify measurement notation and numerical computation, giving indication to the precision of the numbers.
(vi). Unit of Length: The SI Unit of length is meter (m). Various other metric units used for measuring length are related to the meter by either multiples or submultiples of 10.Thus,
Very small distance are measured in micrometer or microns (urn), angstroms (A), nanometer (nm) and femtometre (fm).
For really large distances, the light year is the unit of choice. A light year is the distance light would travel m a vacuum after one year. It is equal to some nine quadrillion meters (six trillion miles). 1 light year .
Base Quantities and Units
Base Quantity |
SI Unites |
|
|
Name |
Symbol |
Length |
meter |
m |
Mass |
kilogram |
kg |
Time |
second |
s |
Electric current |
ampere |
A |
Thermo dynamic Temperature |
kelvin |
K |
Amount of substance |
mole |
Mole |
Luminous |
candela |
cd |
Important Units of Measurement
Used to Measure |
Name of the Unit |
Electric Current |
Ampere |
Wave length of light |
Angstrom |
Electric charge |
Faraday |
Magnetic induction |
Gauss |
Magnetic Flux |
Maxwell |
Electric Charge |
Coulomb |
Electric Resistance |
Ohm |
Electric Tension |
Volt |
Power |
Watt |
Intensity of Sound |
Bell |
Temperature |
Celsius, Kelvin, Farenheit |
Atmospheric Pressure |
Bar |
Quantity of heat |
Calorie |
Force |
Dyne |
Work or Energy |
Joule |
Work |
Newton |
Pressure |
Pascal |
Luminous |
Lumen |
Other Measures
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