Question

What is coherent System in simple words?

Do all systems (MKS , FPS , SI , CGS) coherent?? Yes or No?

If only SI system is coherent then why other systems are not coherent??​

Answer 1

COHERENT SYSTEM:

• Coherent system is based on derived units.

• So to know about coherent system, we should go further with derived units.

Derived units:

• Derived units are those which are derived only from the 7 fundamental quantities otherwise called base quantities.

The seven base quantities are

$\Large\begin{array}{|c| c |c|}\cline{1-3}\cline{1-3}\bf Base\ quantities&\bf Units&\bf Symbols\cline{1-3}\cline{1-3}\sf Length&\sf metre &\sf m \cline{1-3}\cline{1-3}\sf Mass&\sf kilogram &\sf kg\cline{1-3}\cline{1-3}\sf Time&\sf seconds&\sf s\cline{1-3}\cline{1-3}\sf Temperature &\sf kelvin &\sf K\cline{1-3}\cline{1-3}\sf Luminous \ intensity&\sf candela &\sf cd\cline{1-3}\cline{1-3}\sf Amount\ of \ substance &\sf mole &\sf mol\cline{1-3}\cline{1-3}\sf Electric \current&\sf ampere &\sf A\cline{1-3}\cline{1-3}\end{array}$

Examples:

• Also in Coherent system the base quantities with the proportionality constant will be equal to one.

Eg 1. F = ma

When mass = 1 kg and a = 1 m/s² it represents F = 1 N.

Eg 2. P = W / t

When W = 1 J and t = 1 s it represents P = 1 J / s or 1 Watt.

Hence SI is a coherent system.

MKS , FPS , CGS being a subset of SI will also be the coherent system.

CONCLUSION:

• MKS , FPS , SI , CGS are all coherent systems.

EXTRA POINTS:

• MKS - Metre, Kilogram, Second.

• FPS - Foot, Pound, Second.

• SI - System of international.

• CGS - Centimetre, Gram, Second.

• The units named after scientists should be written in small letters while the respective symbols should be in capital letters.

Eg 1. 1 ampere or 1 A.

Eg 2. 2 newton or 2 F.

It should not be written as 2 Newton or 2 n.