Hooks law

It state that;

" When material is loaded within elastic limit then stress is directly proportional to the strain."

Mathematically,

stress	∝ strain
σ	∝ e
σ	= constant X e
σ/e	= constant
constant	= σ/e
E	= σ/e

Where;
             σ - Stress,
             e - Strain,
             E - Elastic constant or Young's Modulus or Modulus of elasticity.