WHAT ARE PHYSICAL QUANTITIES?
There
are some characteristics of every material object. These are to be measured to
specify them. For example to specify the characteristics of a brick, its
length, width, height and mass are to be measured. Such characteristics are
called physical quantities.
Physical
quantities are divided into two categories, base quantity and derived quantity.
(i) Base
quantity: Base quantities are not defined in terms of other physical
quantities such as length, time, mass etc
(ii) Derived
Quantity: Derived quantities are those quantities whose definitions are
based on other physical quantities; for example: volume, density, force etc.
WHAT IS
MEANT BY UNITS?
To measure a physical
quantity, we need to compare it with some standard quantity. While
measuring a physical quantity, we have to see that how many times this quantity
is bigger or smaller than the standard quantity. This standard quantity is called
a unit.
(i) Base
unit: The unit of base quantity is known as base unit such as Kilogram,
Metre, Kelvin, etc. There are seven basic units in system international.
(ii) Derived
unit: The unit of derived quantity is known as derived unit such as Newton , Watt, Joule, etc.
WHAT IS
INTERNATIONAL SYSTEM OF UNITS?
Various standard
units have been in use at different times in different parts of the world. With
the passage of time, these units were made more refined and acceptable. The
eleventh general conference of international committee on weights and measures
recommended that all countries of the world should adopt a system of same kind
of standard units. This conference recommended the use of a system consisting
of seven base units known as international system of units. It is abbreviated
as SI. This is system is in use all over the world.
The units of the derived quantities
can be derived using the seven basic units.
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