Units and measurements Flashcards
Meaurement
process of determining how large or small a physical quantity is as compared to a basic reference standard. This reference standard is called the unit.
how is a unit chosen
can be chosen arbitrarily but should be accepted internationally and should not vary from place to place.
what do we need to know to express a physical quantity
1) the unit in which the quantity is measured
2) the magnitude of the quantity
what are fundamental or base quantities?
they are treated as independent of other physical quantities. Units of such quantities r called fundamental or base units. 7 base quantities. these r length, mass, time, electric current, temp, luminous intensity and amount of substance.
derived quantities
all physical quantities whose units can be defined as a combination of these seven base quantities. example- velocity, acceleration, momentum. etc. units of such quantities r called derived units.
System of Units
a complete set of both base and derived units.
CGS system
centimeter, gram, second for length mass and time respectively.
FPS system
foot, pound, second for length, mass and time respectively
MKS system
meter, kilogram, second for length mass and time respectively.
SI system
General Conference on Weight and Measures made a system of units which is called the SI system and is an abbreviation for Systeme Internationale d’ Unites ( French name for International System of Units.)
1) it is a decimal system , also known as metric sytem, a modernised and extended from of metric systems like CGS and MKS.
2) There are 7 base units and 2 supplemenatry units.
Supplementary angle
1) Plane Angle- ds/r. SI unit is radian respresented as rad.
Total plane angle subtended by and angle at the centre = 2 pi radian.
2) Solid Angle dA/r^2
Si unit is steradian represented ad ‘sr’
BOTH THESE QUANTITIES ARE DIMSENSIONLESS
Measuring lengths of
1) Metre scale
2) Vernier Caliipers
3) Screw Gauge
1) between 10^-3 m to 10^2 m
2) distances abt 10^-4
3) lengths as less as 10^-5 m
thickness of film is approximately equal to the molecular size of the oleic acid,
t is found to be of the order of 10^-9m
thickness of film is aprproximatley equal to the molecular size of the oleic acid.
Thus the diameter the of a molecule of oleic acid is equal to the thickness of the of the film and is about 10^-9 m
unified atomic mass
The unified atomic mass unit is the one-twelfth of the mass of an atom of carbon-12 isotope including the mass of an electrons.
1 u = 1.66 into 10^-27 kg
