physics units and measurements class 11

physical quantities

quantities which can be measured and which can explain and express physical happenings through physical laws is called physical quantities.

fundamental quantities

a division of physical quantities independent from other quantities and is self defining is called fundamental quantities. eg.... length, mass,time

derived quantities

quantities dependent on fundamental quantities or expressed with the help of fundamental quantities. eg.... force density velocity work energy. it can be derived with the help of suitable multiplication or division of different powers of fundamental quantities

quantities

q=n×u
n is no. and u is unit
n1u1=n2u2
n and u are inversely proportional
u2<u1 then n2>n1

unit

internationally accepted arbitrary chosen reference standards used for measurement

fundamental units

units of fundamental quantities. eg....metre,kilogram,second etc

derived unit

units of derived quantities. eg....m/s,N etc

Systems of Units

1. F.P.S system- british system, foot( unit of length), pound( unit of mass), second( unit of time)
1 foot is 30.48 cm, 1 foot is 12 inches, 1 inch is 2.54cm, 1 pound is 0.4536kg

2. C.G.S system- french,centimetre( unit of length), gram( unit of mass), second( unit of time)

3. M.K.S system- french, metre( unit of length), kilogram( unit of mass), second( unit of time)

SI system

this is an extended version of mks system. 7 fundamental quantities plus 2 supplementary quantities
length metre m
mass kilogram kg
time second s
current ampere A
temperature kelvin K
amt of substance mole mol
luminous intensity candela cd
plane angle radian rad
solid angle steradian sr
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plane angle

in a circle the angle formed between two radius is plane angle referred to as theta. used with 2d shapes
theta= arc length/radius
non si unit of plane angle is degree
360°= 2pi rad
1°= pi/180 rad
180°= pi rad
90°= pi/2 rad
60°= pi/3 rad
1 rad= 180/pi °

arc minute and arc second

1° can be divided to 60 parts each part called arc minute
1°=60'
1'=60"
1 arc minute can be divided into 60 arc seconds

solid angle

it's usually used with 3d objects, the angle thus formed is solid angle .
represented as capital omega. small omega is a w.
solid angle=area/radius2
si unit is steradian

SI prefixes

for example, metre is not convenient for long length or short lengths . so we use km for long distances and cm and mm for short distances
1 km=1000m=10^3m

multiple prefixes

10^12 is teta represented by T
10^9 is giga represented by G
10^6 is mega represented by M
10^3 is kilo is represented by k

sub multiple prefixes

10^-1 is deci represented as d
10^-2 is centi represented by c
10^-3 is milli represented as m
10^-6 is micro represented as mu
10^-9 is nano represented as n
10^-12 is Pico represented by p
10^-15 is femto represented by f
10^-18 is atto represented by a
to remember, femto is a prefix and 1 Fermi is a unit for 1 femto metre or 10^-15m
1 angstrom or 1 A° is 10^-10m

instruments for calculating shorter lengths

1. vernier caliper- named after the engineer vernier, it can calculate upto 0.1mm
2. screw gauge- can calculate upto 0.01mm

practical units of length

1. astronomical units(A.U)- it is the average distance between earth and sun. earth revolve around the sun in an elliptical path(proposed by Kepler).
1AU= 1.496×10^11m
2. light years- we know that the light travels in the speed of 3×10^8m/s. the distance travelled by light in a year in the vacuum is light year.
1 light year=9.46×10^15m
parallactic seconds- largest practical unit.
1 par sec=3.08×10^16m
1 par sec=3.26 light years

units of measurement of mass

1 quintal is 100kg
1 tonne is 1000kg
smaller mass is calculated with the help of mass spectrometer.
1 a.m.u=1.66×10^-27kg
1 chandrashekhar limit or 1CSL=1.4×SOLAR MASS
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units of measurement of time

1 min=60s
1h=60 min or 3600s
atomic clock is the most accurate clock
1 shake=10^-8s

basic conversions

1m=100cm=10^2cm
1cm=10^-2m
1cm=10mm=10^1mm
1mm=10^-1cm
1mm=10^-3m
1km=1000m=10^3m
1h=3600s=60^2s
1g=10^-3kg
1kgm/s^2=10^5gcm/s^2 or 1NEWTON(N)=10^5 DYNE
1kgm^2/s^2=10^7gcm^2/s^2 or 1 Joule(J) = 10^7erg