Page 127 - Science Class 06

The ancient units of length as “palm”, A light year is unit of length equal to the
“handspan” and “yard”. These units of distance travelled by light in one year.

length are s ll used to measure the length 1 light year = 9.461 × 10¹⁵ metres
of various objects.
Very small lengths are measured in
STANDARD UNIT OF LENGTH micrometer and micron (m), angstrom (Å),
You have studied that people in ancient nanometers (nm) and femtometer (fm).

me used their footstep, arm length (cubit), Mul ples and Sub-mul ples of the Units of
handspan, ropes, s cks, etc. to measure Length
lengths. But all these units of lengths were
not sa sfactory because length of arm, foot 1 kilometre (km) = 1000 m
3
and handspan vary from person to person. = 10 metre
Therefore, a standard unit for measuring 1 cen metre (cm) = 1/100 m

length as well as other physical quan es
–2
= 10 m
were needed that could be acceptable not
only in one country, but in other countries 1 millimetre (mm) = 1/1000 m
as well. = 10 m
3
–
A standard unit means a unit that is 1 micron (m) = 1/1000000 m
acceptable world wide. However, several – 6
systems of unit have been in use for the = 10 m
measurement. The common systems are 1 nanometre (nm) = 1/1000000000
the CGS (Cen mtre, Gram, Second); FPS = 10 m
9
–
(Foot, Pound, Second) which is acceptable
Some Common Measuring Devices of
in the Bri sh system.
Length
Ruler, metre rod, measuring tape, etc. are

some common measuring devices of length.
In India, all the na onal standard units HOW TO MEASURE LENGTH?

are maintained by the Na onal Physical
Laboratory (NPL), New Delhi. Have you ever thought that what is the
length of your science book? Let’s measure
The SI unit of length is metre. In 1989, the length of a book using a ruler.
the standard metre was defined as the

distance between two lines marked on a
pla num–iridium rod preserved at constant
temperature and pressure. It is preserved at
the Interna onal Bureau of Weights and
Measure in France.

Large distance such as the distance of the

sun from the earth is measured in light year. Measuring Tape

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