The extension of a material divided by its original length is called

• A. Elasticity
• B. Strain
• C. Stress
• D. Deformation

Answer: (B)

Strain is the extension divided by the original length. It tells you how much a material stretches relative to where it started, and it’s calculated as ΔL divided by L0. This yields a dimensionless quantity (often shown as a fractional value or percent). This differs from stress, which is the force per unit area causing the deformation; deformation is the actual change in size or shape (the ΔL). Elasticity describes how well a material returns to its original dimensions after loading. Because the question asks for the ratio of extension to original length, the correct term is strain.