What law states that the stress in an elastic body is directly proportional to the strain?

The law that states that the stress in an elastic body is directly proportional to the strain is known as Hooke's Law. This fundamental principle in materials science and engineering describes the behavior of elastic materials when they are subjected to forces. When a material is within its elastic limit, it will return to its original shape after the load is removed, and the relationship between stress (force per unit area applied to the material) and strain (deformation or displacement resulting from the applied force) is linear.

Hooke's Law can be mathematically expressed as σ = E * ε, where σ represents the stress, E is the modulus of elasticity (a material property), and ε represents the strain. This relationship is critical in fields such as structural engineering, mechanical engineering, and materials science as it helps predict how materials will behave under various loading conditions.

The other options refer to related concepts. Young's Modulus and the modulus of elasticity are terms often used in conjunction with Hooke's Law; however, they specifically represent the proportionality constant (E) and are not laws themselves. They are important for quantifying the stress-strain relationship but do not state the proportionality principle directly. Hence, Hooke's Law is the correct answer to the question posed