A physical quantity is a quantity that can be measured like length, mass, time, temprature, area, volume and density etc. Physical quantites are of two types
- Basic physical quantities
- Derived physical quantities
Basic physical quantities
Physical quantities which are independent of other physical quantites are known as basic physical quantaties. Their are 7 basic physical quantites:-
Mass, Length, Time, Luminous Intensity, Temprature, Electric Current and amount of substance.
Basic physical quantities are also known as Fundamental Physical Quantites.
- Mass (Kilogram): Kilogram is the SI UNIT (International System of Units) of mass. Kilogram is denoted by the symbol kg, gram is denoted by g and milligram by mg, 1mg=1/1000 gram and 1 gram=1/1000 kg.
- Length (Metre): Metre is the SI UNIT of length. A metre is the length of path travelled by light in vaccuum during the time interval of 1/299792458 of a second. 1 km=1000 metres, 1 cm=1/100 metres
- Time (Second): Second is the SI unit of time. 60 sec=1 min, 60 min=1 hour, 24 hours=1 day
- Temprature (Kelvin): Kelvin is hte SI unit of temprature. The tripple point of water is temperature at which all three phases ie. ice, liquid and water vapour can co-exist is273.16 kelvin. The Kelvin is 1/273.16 of the Triple point of water.
- Luminous Intensity (Candela): Candela is the SI unit of Luminous Intensity. Luminous intensity means brightness of light
- Electric Current (Ampere): Ampere is the SI Unit of electric current.
- Amount of Substance (Mole): Mole is the SI unit of the amount of substance. A mole contains same amount of prticles as 12 gm of carbon-12 contains
Derived physical quantities
A Physical Quantity expressend in terms of 2 or more fundamental units are called Derived Physical Quantities. It is obtained by dividing or multiplying one basic physical quantity with another basic physical quantity.
eg: Speed, Area, Energy, Force, Frequency, Heat, Velocity, Wavelength etc.
Unit of speed=Unit of distance/Unit of time (m/s or ms-1).