# Constants In Physics

Constants in physics synonymous to physical constants sometimes Universal constants or fundamental physical constants is the physical quantity or entity which are believed to have a constant value in time and are universal in nature.

## Nature Of Physical Constants

Based on nature, the fundamental constants are grouped into three categories namely-

• A: Characteristic of a particular system. (Characteristic of light)
• B: Characteristic of a class of physical phenomena. (Characteristic of electromagnetic phenomena)
• C: Universal Constants. (Discovered after the discovery of special relativity)

Few Physical constants are can take the dimensional form like – speed of light, in contrast, few are dimensionless like- fine structure constant. Some physical constants are material constants which means they possess constant value for a material.

A constant can be expressed using multiple equivalent units like – SI, natural units, atomic mass unit, CGS units etc. Some physical constant redefined by fixing the SI values. But this certainly increases the uncertainty in the value of physical constants.

## Number Of Fundamental Constants

There is no ground rule defining the number of physical constants in physics. The number varies in accordance with the accepted physical theory.

### The table given below comprises of the list of physical constants –

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#### Practise This Question

When the tension in a metal wire is T1, its length is l1. When the tension is T2, its length is l2. The natural length of wire is