Any physical quantity has a definite magnitude of a quantity that is called unit. Units are two types: fundamental unit and derived unit.
Physical Quantity |
S.I Unit & Symbol |
Length | Metre(m) |
Mass | Kilogram(Kg) |
Time | Second(s) |
Temperature | Kelvin(k) |
Electric Current | Ampere(A) |
Luminous Intensity | Candela(cd) |
Amount of Substance | Mole(mol) |
Angle | Radian(rad) |
Solid Angle | Steradian(sr) |
- The unit of long distance or astronomical distance is Light Year (प्रकाश वर्ष).
1 Light Year = 9.46 x 10^{15 }metre - Parsec is the highest unit for distance measurement.
1 Parsec= 3.26 light year = 3.08 x 10^{16 }metre - The S.I unit of Force is Newton (N).
- C.G.S unit of Force is Dyne.
1 N = 10^{5 }Dyne - S.I unit of Work is Joule
- C.G.S unit of Work is Erg
1 Joule= 10^{7 }Erg
There are two types of Physical Quantity:
- Scalar Quantity: Which quantity has only magnitude and that doesn’t have direction, i.e. called scalar quantity.
Ex: – Distance, speed, current, Temperature, Pressure etc.
- Vector Quantity: Which quantity has magnitude with direction, i.e. called vector quantity.
Ex: – Displacement, velocity, force, acceleration etc.
- Distance is always +ve. But Displacement is +ve, -ve or zero.
- Speed= distance/time, I unit= metre/second or m/s.
- Velocity (v) = dx/dt = rate of change of displacement with respect to time
S.I unit= m/s - Acceleration (a) = dv/dt= rate of change of velocity with respect to time.
S.I unit= m/s^{2 }[If the velocity of a body is reduced with time i.e. called retardation or –ve acceleration.] - Force(F)= ma
(m= mass of object, a= acceleration)(S.I unit= Newton (N) or Kg m/s^{2})
Energy has two types:
- Potential Energy (P)= mgh ; m= mass, g=gravity, h=height
[ S.I unit= Joule(J)] - Kinetic Energy (K.E)= (½)mv^{2} ; v=velocity, m= mass;
[S.I unit= Joule] {Joule(J)= Kg m^{2}/s^{2}} - Momentum(P)= Mass x velocity [ S.I unit= Kg m/s]
- Density(d)=mass/volume(m/v) [S.I unit= Kg/m^{3 }]
- Pressure: It is defined as a Force of one Newton per square metre. S.I unit of Pressure is Pascal(Pa).
The conversion between atm, Pa, and torr is:-
1 atm = 101325 Pa = 760 torr.
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