It is comparison of an unknown physical quantity with the known or standard quantity.
For e.g: While measuring the length of a book, it is compared with the known length of scale.
Significance of Measurement
Physical Quantities
They are the one that can be measured directly or indirectly regarding their quantity and quality.
For example: Mass is the physical quantity, which can be measured using pan balance or beam balance.
Types of Physical Quantities
Units
The standard reference quantity with reference to other physical quantities of same kind are measured is called unit.
For eg: Unit of kilogram is Kg. If we measure mass to be 7 kg, it means that the measured mass is 7 times greater than the standard reference quantity.
They are of two types, Fundamental and Derived Unit
Difference between Fundamental Units and Derived Units.
Fundamental Units |
Derived Units |
They are the units that do not depend upon other units. |
They are the units that depend upon other units. |
Also called as basic or Independent units. |
Also called as Dependent units. |
There are seven fundamental units. |
There are large numbers of derived units. |
Reasoning Concepts
Velocity has its unit meter per second which is a derived unit that it is obtained from fundamental units meter (length) and second (time).
Unit of velocity = \(\frac{Unit \; of \; length}{Unit \; of \; time}\) = \(\frac{meter}{sec}\) or \(\frac{kilometer}{hour}\)
Questions:
System of Units
System of writing different units in different parts of the world makes the measurement activities quite difficult as the world is becoming a single global market.
To make uniformity in measurement, following systems have been developed:
However, these three systems can only explain about the units of length, mass and time but not other fundamental physical quantities like Temperature, electric current, Amount of substance and frequency. So, the scientists have developed standard International system of units in which all seven physical quantities and their units are included.
SI system of units is the world – wide accepted system of units used in all forms of scientific activities that is the extended form of MKS system. Full Form of SI Units: System of International De – Units
Difference between M.K.S. and SI System of Units.
M.K.S. System |
S.I System |
It is a metric and simple system of measurement. |
It is the extended and revised system of SI system. |
It involves three fundamental quantities length, mass and time. |
It involves all seven fundamental quantities. |
Significance of SI system
Reasoning Concepts
Table Showing SI units of different physical quantities:
Physical Quantities |
SI Units (Symbol) |
Length |
Metre (m) |
Mass |
Kilogram (kg) |
Time |
Second (sec) |
Current |
Ampere (A) |
Temperature |
Kelvin (K) |
Frequency |
Hertz (Hz) |
Intensity of Light |
Candela (Cd) |
Amount of Substance |
Mole |
Work |
Joule (J) |
Energy |
Joule (J) |
Power |
Watt (W) |
Pressure |
Pascal (Pa) or N/m^{2} |
Force |
Newton (N) |
Velocity |
m/ sec |
Acceleration |
m/sec^{2} |
Potential Difference |
Volt |
Resistance |
Ohm |
Questions