The document discusses different methods of measuring length. It describes using meters as the standard unit of length and using other units like feet and inches for measuring specific lengths. It also discusses using kilometers to measure vehicle distances. For very large distances that can't be measured with standard instruments, the document covers using the parallax method and echo method, with the parallax method utilizing angle measurements and the echo method calculating distance based on the time it takes for a sound to return. The document notes the wide range of lengths that can be measured, from microscopic scales like atoms to macroscopic scales like the size of the universe.

1. Measurement of Length

2. Length
 Length is a fundamental quantity which we use to
measure different size of objects
 The standard unit of length is meter
 We use units of length preference wise, so that
our measurements are precise and accurate

3. Measurement of Length
 We use different units to measure different
lengths
 For example, we make use of feet and inches to
measure our height
 We use kilometer to measure the distance
travelled by our vehicle

4. Measurement of Large Distance
 There are certain distance which can’t be
measured with the help of scales and instruments
 To measure large distances we use two special
methods
 Parallax method
 Echo Method

5. Parallax method
 In this method we use the parallax principal,
which means measuring the displacement
caused by two observation point of view relative
to each other
 The arc length formula is used to measure large
distances in this method

6. Echo Method
 This method involves the echo concept, which
depicts that sound comes back after reflection
 We measure the distance travelled by sound in a
specific time interval to measure distance of a
certain building or a hill
 Speed = 2 × Distance/ Time, is used to measure
the distance D in echo method

7. Range of Length
 The range of measurement of length is quite wide
and varies from microscopic level to the
macroscopic one
 For example size of atoms and molecules is 10-
14m
 The size of universe is around 1026 m

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