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Standard XI
Physics
NCERT
Question

Precise measurements of physical quantities are a need of science. For example, to as certain the speed of an aircraft, one must have an accurate method to find its positions at closely separated instants of time. This was the actual motivation behind the discovery of radar in World War II. Think of different examples in modern science where precise measurements of length, time, mass etc. are needed. Also, wherever you can, give a quantitative idea of the precision needed.

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Solution
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Precise measurement of physical quantity is truly needed.
For example,
1) Ultra-shot laser pulses (time interval 1015 s) are used to measure time intervals in several physical and chemical processes.

2) X-ray spectroscopy is used to determine the inter-atomic separation or inter-planer spacing.
3) The development of mass spectrometer helps to measure mass of atom precisely.

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