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# 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 - CBSE (Science) Class 11 - Physics

#### Question

Precise measurements of physical quantities are a need of science. For example, to ascertain 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.

#### Solution 1

It is indeed very true that precise measurements of physical quantities are essential for the development of science. For example, ultra-shot laser pulses (time interval ∼ 10–15 s) are used to measure time intervals in several physical and chemical processes.

X-ray spectroscopy is used to determine the inter-atomic separation or inter-planer spacing.

The development of mass spectrometer makes it possible to measure the mass of atoms precisely.

#### Solution 2

Extremely precise measurements are needed in modem science. As an example, while launching a satellite using a space launch rocket system we must measure time to a precision of 1 micro second. Again working with lasers we require length measurements to an angstrom unit (1 A° = 10-10m) or even a fraction of it. For estimating nuclear sizes we require a precision of 10-15 m. To measure atomic masses using mass spectrograph we require a precision of 10-30kg and so on.

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#### APPEARS IN

NCERT Solution for Physics Textbook for Class 11 (2018 to Current)
Chapter 2: Units and Measurements
Q: 21 | Page no. 37

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Solution 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 Concept: Significant Figures.
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