SI units, Derived Units : MKS, CGS, FPS system: IIT-JEE Physics Classes
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Hello Friends,Today we will learn about units
and Si units.. We will cover-
What are units?.. The distance between these two points is 2
centimetre..so here centimeter is the unit of the distance ..
Kilometer and miles are big units.. We use Km and miles to measure distance between
two cities.. centimetres and millimetres are small units.. We use these 2 units to measure small distances.. What is MKS system?…
M is for meter , K is for kilogram and S is for Second. So this system is actually based on 3 units,
meter kilogram and second.. Here we measure length in meter, time in second,
same way we measure mass in kilogram..symbols for them are m, s, kg.. Equation of Area is length x width.. so its
unit would be meter x meter..it becomes meter squared.. Formula of volume is length x width x height,..so
meter x meter x meter so unit of volume is meter cubed.. Next system is CGS system..this system is
used to measure small quantities..C for centimeter, G for gram and S for second..here length is
measured in centimeter, its symbol is cm, mass is measured in gram and its symbol is
‘g’.. the time is measured in second, its symbols is ‘S’.. area
is measured in centimeter square..we’ll use again
length x width..so cm x cm..that equals centimetre
squared..and for Volume=Length x width x height..that=centimetre x centimetre x centimetre ..that
equal centimeter cubed..this symbol is used to write exponents.. Length is measured in foot or feet..keep in
mind foot or feet are same things..its symbol is ‘ft’.. Mass is measured in ‘pound’…its symbol
is ‘lb’..time is measured in ‘second’..its symbol is ‘S’..Area is measured in foot
x foot , that is foot squared..Volume is measured in foot x foot x foot , that is foot cubed.. What
are SI units?.. First
fundamental unit is meter which is used to measure Length..Second
is kilogram which is used to measure Mass.Third unit is second which is used to measure time.. Fourth is ampere which is used to measure
electric current..fifth is Kelvin which is the used to measure Temperature..sixth is
mole which is used to measure amount of substance.. Candela for luminous intensity.. And 2 more supplementary units which are added
later.. First is Radian which is unit of plane Angle. Second is Steradian which is unit of Solid
Angle. Derived units ..
We have learnt 7 fundamental units and base units.. Meter per second Is the derived unit because
this unit is made of metre and second..same way Metre per second squared is also made
by metre and second time second..so these units are made by base units or fundamental
units ..so these units are called as derived units..let’s take an Example so how to derive
unit of velocity..for that we need to use formula of velocity ..that is distance over
time..here We will plugin SI unit of distance and SI unit of time that is second..derived
unit of velocity is meter per second..we can derive units of Any quantity using this method..let’s
take another example for acceleration you know formula of acceleration equals change
in velocity over change in time.. So what will we do here, we plug in SI unit
of velocity that is metre per second then SI unit of time that
is second .. Let’s take another example of force.. formula
of force equals mass x acceleration..plug in SI unit of mass which is kilogram.. SI unit of Acceleration that we found meter
per second squared.. There are a few units which has special names
instead of writing them in fundamental units.. Like force.. We don’t write unit of force as kg-m/s^2..instead
we write ‘Newton’.. Same way derived units of energy
is kg-m^2/S^2.. But we generally use special name for unit
of energy that’s ‘joule’..same way special name for unit of Power is Watt. I strongly recommend that you note down all these special names of units
for future reference… I hope, You understand this topic now in better
way.. if you have any question on this topic, please ask questions in the comments box which
is given below..Don’t forget to Subscribe , Share and Likes for daily updates.. thank
you..

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