what is Young's Modulus? Its unit? and where is it used?

Answer 1

Within the elastic limit of any material it is seen that the stress in the material is directly proportional to the strain.
Hence the constant for the proportinality is called Youngs Mdulus (E). The unit of Youngs Modulus is N/mm^2 or MPa(Mega Pascals) or PSI(Pounds per sq. inch) same as the unit of stress.

Also it may be referred as Stress/Strain= Youngs Modulus.

Usage of youngs modulus:
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Stress is not a straight measurable quanitity, but engineers are very curious to evaluate stresses in a loaded material to check if it can withstand the design load or applied load. Strain is a measurable quantity (strain gages can measure strains) and once strain is measured the stress can be deduced by multiplying with the youngs modulus.

Answer 2

Unit For Young's Modulus

Answer 3

The Young's modulus (or Elasticity modulus) is a measure of stiffness of a given material. It can be determined by the slope of the stress-strain curve obtained from tensile tests.

The SI unit of the elasticity modulus is Pa (Pascal). Take a look at the link from Wikipedia for this subject, it's very clear and easy to understand, in my opinion.