Physics | Units and Measurements part 2 | for competitive exams

S.I system:

• S.I stands for → International System of Units.

• S.I system of units has seven base(fundamental) units and two supplementary units.

• In S.I system, there are derived units also.

Fundamental units (Base units):

S. No.	Physical Quantity	SI Unit	Symbol
1.	Length	meter	m
2.	Mass	kilogram	kg
3.	Time	second	s
4.	Electric current	ampere	A
5.	Thermodynamic temperature	kelvin	K
6.	Luminous intensity	candela	Cd
7.	Amount of substance	mole	mol

Supplementary units:

S. No.	Physical Quantity	SI Unit	Symbol
1.	Plane angle	radian	rad
2.	Solid angle	steradian	sr

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Some important points:

→ Distance is defined as the total length of the actual path travelled by an object during its motion.
→ Displacement is defined as the shortest distance between an object's initial and final positions in a definite direction.
→ The SI unit of displacement is meter(m).

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Dimensional formula:

General formula → M^aL^bT^c
           Where M → mass
                        L → length
                        T → time
                   a,b,c → constants
→ M¹ can be written as M, L¹ can be written as L and T¹ can be written as T.
Example:
→ The dimensional formula of mass density is M L^-3 T⁰

$\mathrm{Density}=\frac{\mathrm{Mass}}{\mathrm{Volume}}$

             $=\frac{M}{L^3}$

              = M L^-3

              = M L^-3 T⁰ (there is no time, so we write T⁰ )

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