Physics and Measurement
Physics and Measurement PDF Notes, Important Questions and Synopsis
SYNOPSIS
 Physics domain:
 Macroscopic domain: This includes phenomena at the laboratory, terrestial and astronomical scales. Classical mechanics deals with the macroscopic domain.
 Microscopic domain: This includes atomic, molecular and nuclear phenomena. Quantum mechanics deals with the microscopic domain.
 Four fundamental forces of nature:
Force 
Relative strength 
Range 
Gravitational force 
10^{39} 
Infinite 
Nuclear force (weak) 
10^{13} 
Very short, subnuclear size 
Electromagnetic force 
10^{2} 
Infinite 
Nuclear force (strong) 
1 
Short, nuclear size 
 Physical quantities:

Measure of physical quantity (Q) = numerical value of physical quantity (n) × size of unit (u) n_{1}u_{1} = n_{2}u_{2} = constant

Fundamental quantities, SI unit and their symbols:
Fundamental quantity
SI unit
Symbol
Length
metre
m
Mass
kilogram
kg
Time
second
s
Electric current
ampere
A
Temperature
kelvin
K
Amount of substance
mole
mol
Luminous intensity
candela
cd
 Conversion of units:
Consider dimensions of a physical quantity as ‘x’ in mass, ‘y’ in length and ‘c’ in time. If the fundamental units in one system are M_{1}, L_{1} and T_{1} and in another system are M_{2}, L_{2} and T_{2},
then
 Analysis of dimensional correctness:
Every equation should be dimensionally balanced. This is called ‘principle of homogeneity’. The dimensions of each term must be the same on both sides of the equation.  Principle of homogeneity:
According to the principle of homogeneity, dimensions of all terms in a physical expression should be the same.  Errors:
Errors are classified as (i) systematic errors and (ii) random errors.
 If x_{1}, x_{2}, x_{3} … xn are the measured values of quantities in several measurements, then the mean is
 Absolute errors in measured values are
 If the quantity Z is expressed as a product of quantities A and B, then the maximum fractional error in Z is given by
 If Z = AxByCz, then the maximum fractional error in Z is
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