Page 106 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

A metre scale is divided into 100 equal parts. The Metre
length of each part is one centimetre (cm). This is
One metre is the length between
useful in measuring a length which is less than one
two markings in the sample rod
metre.
made by adding 10% iridium in
platinum and preserved at 0 C at
o
the International Bureau of Weights
and Measures in Paris.
Fig 8.3
Observe the figure showing a part of a scale. The length of the scale made by
Now you know that the length between two comparing its length with this
sample rod is considered to be one
successive long lines is 1 cm.
metre.
Observe the short lines in between two successive
long lines. According to the modern definition
one metre is the distance travelled
Into how many equal parts is 1 cm divided?
by light in vacuum in 1/299792458
What is the use of such a division? second. This new definition has
1 cm is divided into ten equal parts. The length of been accepted for getting better
each part is one millimetre. This becomes useful to accuracy.
measure a length which is less than one centimetre.

1 m = 100 cm
1 cm = 10 mm
If so, find out how many mm is 1m.

Draw a line segment of length 8 cm in your science diary and
mark the following.
PQ = 6 mm

PR = 16 mm
P Q R S
PS = 5 cm
Fig 8.4
The smallest length that can be accurately measured using a
metre scale is its least count. Find it out and record it in your
science diary.

Thickness of a paper

Can you measure a length less than a millimetre using a metre
scale? For example, let’s see how we can measure the thickness
of a sheet of paper.
Take 100 sheets of paper and pile it up to make a bundle.
Measure the height of this bundle using a scale. If it falls in
between two markings, make suitable changes in the number
of sheets. Then measure its height.
Basic Science VIII 105