Question

Problem 1. Explain the definition of the unit of quantity, the definition of SI, and the basic unit of SI and about SI unit system.

Also, select one of the SI basic units and explain the definition of the unit in detail.However, write itdown so that high school students can understand it. Summarize the above in A4

Answer 1

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The definition of quantity and units

The quantity is the amount or numerical value, while the unit is the measurement. For example, if a you buy a packet of bread that contains 150 grams, the quantity is 150 while the unit is grams. In this instance, the quantity is always a number and the units are any measure, such as grams, liters, degrees, lumens, etc.

The definition of SI

The International System of Units (SI, abbreviated from the French Système international (d'unités)) is the modern form of the metric system. It is the only system of measurement with an official status in nearly every country in the world. I was established in 1960 and continuously updated since then.

Basic units of SI and SI unit system

There are 7 base units for 7 distinct quantity and from called independent units and all other units are derived using two or more base units.

Base units

1. The unit of time is second with symbol S.

2. Unit of mass is Kilograms with kg

3. Unit of current ampere (electric current, A),

4. Unit of thermodynamic temperature, Kelvin, K

5. Unit of amount of substance, mol ,m.

6. Unit of (luminous intensity, cd)

7. Unit of length is metre with m.

Derived units.

Units made with the help of above 7 base units. For example acceleration is a derived unit which is m/s^2 made up of m(meter) the unit of length and s(second) the unit of time.

The definition of unit of mass (kg)

The definition of units keep evolving. The unit of mass(kg) has been redifined many times as below-

1793: The grave (the precursor of the kilogram) is defined as the mass of 1 litre (dm3) of water, which was determined to be 18841 grains.

1795: the gram (1/1000 of a kilogram) was provisionally defined as the mass of one cubic centimetre of water at the melting point of ice.

1875-1889: The Metre Convention is signed in 1875, leading to production of The International Prototype of the Kilogram (IPK) in 1879 and its adoption in 1889. It had a mass equal to the mass of 1 dm3 of water under atmospheric pressure and at the temperature of its maximum density, which is approximately 4 °C.

The present definition

2019: as of 20 May, the kilogram is redefined in terms of the Planck constant as approved by the General Conference on Weights and Measures