In Hooke's Law δ = PL/AE, what does the symbol E represent?

• A. Elastic constant of the material
• B. Length of bar
• C. Cross-sectional area
• D. Modulus of Elasticity (Young's Modulus)

Answer: (D)

In axial deformation, the symbol E represents the Modulus of Elasticity, also called Young's modulus, which measures a material’s stiffness. Stress is P divided by A, and strain is δ divided by L, and Hooke’s law in tensile form is σ = Eε. Rewriting this and substituting σ = P/A and ε = δ/L gives δ = (P L) / (A E). This shows E is a material property that links how much a bar stretches to the applied load, independent of its shape—unlike L and A, which are geometric. The other terms in the equation (L and A) are geometry factors, not the material’s stiffness, and “elastic constant” is not the precise standard name for this property. Therefore, the correct concept is the Modulus of Elasticity (Young's modulus).