Units And Measurements Flashcards
Physical quantity
Any quantity that can be measured directly or indirectly
Fundamental Quantities
Quantities which cannot be expressed in terms of simpler quantities and are independent of other physical quantities
7 fundamental quantities
Length Mass Time Temperature Electric Current Luminous Intensity Amount of Substance
Derived quantities
Quantities which are derived from different combinations of fundamental quantities
Units of fundamental quantities
Fundamental Units
Units of derived quantities
Derived units
System of units
A system of units is a complete set of units that are needed to measure all fundamental and derived quantities
Examples of systems of units (4)
CGS
MKS
FPS
SI
SI unit
SI units are a common system of units that are internationally accepted. It is based on seven fundamental units and two supplementary units
SI unit is based on?
Seven fundamental units and two supplementary units
SI unit of Mass
kg
SI unit of length
m
SI unit of Time
s
SI unit of Electric Current
A
SI unit of Temperature
K (Kelvin)
SI unit of Amount of Substance
mol (moles)
SI unit of Luminous Intensity
cd (candella)
Plane Angle
Radian
Solid Angle
Steradian
Advantages of SI system (3)
Rational
Metric
Coherent
SI units are rational?
Each quantity only has one unit
SI units are metric?
The multiples and sub-multiples of SI units are in powers of 10
SI units are coherent?
Simple multiplication and division of fundamental units can be used to obtain all derived units without any numerical factor
Dimensions
Dimensions are the powers to which fundamental quantities are to be raised to represent any given physical quantity
Dimensional Constants
g, G
Dimensionless Constants
π, 1/2, 2…
Dimensional Variable
Pressure, Work..
Dimensionless Variables
Plane Angle, refractive index…
1st application of dimensional analysis
To check dimensional correctness or consistency of equations
2nd application of dimensional analysis
To derive relationships among different physical quantities
Dimensional correctness aka?
Dimensional consistency
Principle of homogeneity
The principle of homogeneity states that a physical equation will only be correct if the dimensions of all the terms on either side are the same. Only terms that have the same dimensions can be added or subtracted.
1st limit of dimensional analysis
Dimensional analysis does not give any information about the proportionality constant
2nd limit of dimensional analysis
It fails when a physical quantity depends on more than three other quantities
3rd limit of dimensionless analysis
It fails when a physical quantity is a sum or difference of other quantities.
4th limit of dimensional analysis
It fails to derive relationships which involve dimensionless quantities like trigonometric functions
Limitations of dimensional analysis (4)
Proportionality constant
Dependent on more than three other quantities
Sum or difference of other quantities
Dimensionless like trig
Significant digits
Significant digits are those digits in a measurement which are known to be reliable and the first unreliable digit
Accuracy
Accuracy is the closeness of the measured value to the true value of the quantity
Precision
Precision is the resolution to which a quantity can be measured
