Strain is:

Strain is:

• A. The internal resistance to external force.
• B. The measure of the acidity of a solution.
• C. The proportional dimensional change that occurs when a stress is applied; a total elongation per unit length, and it may include elastic and plastic components.
• D. A void left in cast metals during solidification.

Answer: (C)

Strain is the measure of how much a material deforms when a load is applied. It’s the proportional change in length per unit length, written as delta L divided by L0, so it’s a dimensionless quantity (often expressed as a percentage). The key idea is that strain captures the material’s deformation, which can include both elastic (reversible) and plastic (permanent) parts, so the total strain reflects overall elongation per unit length. This is why the description that mentions a proportional dimensional change under stress—and that it may include both elastic and plastic components—best fits what strain is. The other descriptions don’t fit: internal resistance to external force describes stress or strength, not deformation; acidity is a pH measure; and a void left in cast metals during solidification refers to a defect like porosity, not deformation under load.

Strain is the measure of how much a material deforms when a load is applied. It’s the proportional change in length per unit length, written as delta L divided by L0, so it’s a dimensionless quantity (often expressed as a percentage). The key idea is that strain captures the material’s deformation, which can include both elastic (reversible) and plastic (permanent) parts, so the total strain reflects overall elongation per unit length. This is why the description that mentions a proportional dimensional change under stress—and that it may include both elastic and plastic components—best fits what strain is.

The other descriptions don’t fit: internal resistance to external force describes stress or strength, not deformation; acidity is a pH measure; and a void left in cast metals during solidification refers to a defect like porosity, not deformation under load.