Definitions [14]
Define mass Mention its unit.
Mass is the amount of matter contained in a body. Its unit is a kilogram (kg).
Define the term density of a substance.
The density of a substance is defined as the mass of a unit volume of that substance.
`"Density" = "Mass"/"Volume"`
Define one metre, the S.I. unit of length. State it's one multiple and one submultiple.
One metre is defined as the distance travelled by light in the air in `1/(299,792,458)` of a second.
The S. I. unit of length is meter.
Multiple of metre = Kilometre (km).
Submultiple of metre = Centimetre (cm)
A value, quantity, or magnitude in terms of which other values, quantities, or magnitudes are expressed is called a unit.
The smallest value up to which an instrument can measure is called the least count.
Units that are neither fundamental nor derived but are accepted in the SI system (e.g., radian for plane angle, steradian for solid angle) is called supplementary units.
Units that are derived from fundamental units — such as force, which is mass × acceleration — and are expressed algebraically using base units is called derived units.
The basic physical quantities that cannot be derived from other quantities and serve as the foundation for all measurements is called fundamental quantities.
The quantities that are derived from fundamental quantities through mathematical relationships is called derived quantities.
A quantity that can be measured by an instrument and through which we describe the laws of the physical world is called a physical quantity.
A set of particular physical quantities from which different other units can be obtained, which are neither derived from one another nor resolved into any other units is called fundamental units.
The weight of an object is defined as the force with which the earth attracts the object.
Mass is the amount of matter present in the object. The SI unit of mass is kg.
The basic physical quantities that cannot be derived from other quantities and serve as the foundation for all measurements is called fundamental quantities.
Formulae [1]
Least count = \[\frac {\text {Smallest reading on main scale}}{\text {No. of divisions on main scale}}\]
Instrument Least Count = \[\frac {\text {Main scale least count}}{\text {Divisions on secondary scale}}\]
Key Points
The SI system has 7 base units:
| Base Quantity | Name | Symbol |
| Length | metre | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric Current | ampere | A |
| Thermodynamic Temperature | kelvin | K |
| Amount of Substance | mole | mol |
| Luminous intensity | candela | cd |
Temperature Conversions:
K = °C + 273.15
\[°F=\frac{9}{5}°C+32\]
