System of Units: MKS, CGS, FPS and SI-Units

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Units and MeasurementReference Notes – System of Units
Unit: Units and Measurement
Science | Physics Class 11

Different systems of units are used to perform measurement. The different systems of units are explained below:

  1. MKS-System: In this system, length is measured in Meter (M), mass is measured in Kilogram (K) and time is measured in Second (S).
  2. CGS-System: In this system, length is measured in centimeter (C), mass in gram (G) and time in second (S).
  3. FPS-System: In this system, length is measured in foot (F), mass in pound (P) and time in second (S).

In this system, seven basic and two supplementary units are taken. The fundamental quantities adopted by the SI-units, their units and symbols are given below:

Units of Fundamental Quantities:

Fundamental QuantityUnitSymbol
Luminous intensitycandelacd
Amount of substancesmolemol

In addition to the above seven fundamental units in SI-units, two supplementary units are also defined. These supplementary units are given in the table below:

Plane Angleradianrad
Solid anglesteradiansr

Definitions of SI Base Units:

  1. Metre: The meter is defined as the length of the path travelled by light in a vacuum during a time interval of 1/299,792,458 of a second.
  2. Second: The second is the duration of 9,162,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atoms.
  3. Kilogram: The kilogram is the mass equal to the mass of standard platinum-iridium alloy cylinder (90% platinum and 10% iridium) kept at the International Bureau of Weights and Measures in Paris. This cylinder is about 4 cm high and 4 cm in diameter.

Advantages of SI-Units:
The advantages of SI-Units are given below:

  1. It is a rational system of units.
  2. It is a coherent system of units.
  3. It is a decimal system.
  4. It is highly useful in practical and theoretical work.

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One Comment

  1. Akshay
    Posted September 2, 2017 at 9:32 pm


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