Which of the following is dimensionless?

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SSC Matric Level Previous Paper (Held on: 2 Feb 2022 Shift 3)
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  1. Longitudinal stress
  2. Shear stress
  3. Deforming force
  4. Longitudinal strain

Answer (Detailed Solution Below)

Option 4 : Longitudinal strain
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The correct answer is Longitudinal strain.

Key Points

CONCEPT:

  • The powers to which fundamental quantities must be raised in order to express the given physical quantity are called its dimensions.
  • A quantity without dimension will usually be a ratio of two quantities with similar dimensions and, hence, cancel out.
  • Thus, they will have no units.

EXPLANATION:

  • Longitudinal stress:
    • Longitudinal stress is the stress which acts along the length and its unit is N/m2 or Pascal.
  • Shear stress: 
    • If the deforming force acts tangentially to the surface of the body, It produces a change in the shape of the body.
    • This tangential force applied per unit area is called shear stress.
    • Its unit is  N/mm2 or MPa. 
  • Deforming force: 
    • Deforming Force An external force applied to a body that changes its size or shape or both is called deforming force.
    • its unit is N or kg-m/s2.
  • Longitudinal strain: 
    • The change in the length (ΔL) to the original length (L) of the body is known as longitudinal strain.

i.e., \(Longitudinal\;strain = \frac{{{\rm{\Delta }}L}}{L}\)

  • And since it is a ratio of two lengths, hence it is a dimensionless quantity.
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