Page 112 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

Derived Units

Let’s try to find the area of a classroom of length 5 m and breadth
4 m
Area = length × breadth = 5 m × 4 m = 20 m 2

From the answer obtained, can you find out the unit of area? Is
the unit of area included in the table of fundamental units?
How did you calculate the unit of area?
Unit of area = unit of length × unit of breadth

= m × m = m 2
You might have understood that the unit of area is stated using
the fundamental unit of length. Such units expressed using
fundamental units are derived units.
Units which are expressed in terms of fundamental units or
those units which are dependent on fundamental units are
derived units.

On the basis of the above information, let’s take a look at the
salient features of SI units.
Unified units
Internationally accepted

Adequate to express all physical quantities.
Can you find the area of a surface having irregular edges using
the method adopted to find the area of your class room? Let’s
look at the example of finding the area of a leaf.
Area of a leaf

Let's find out the area of a leaf. Take the leaf and place it on a
graph paper and trace the outer edges using a pencil.

Fig 8.16

Basic Science VIII 111