A steel wire of length 4 m and cross-sectional area 2 × 10-6 m2 is stretched by 0.4 mm. If the force applied is 200 N, w
Young's modulus: Y = (F L) / (A ΔL). Substitute: ΔL = 0.4 × 10-3 m. Y = (200 × 4) / (2 × 10-6 × 0.4 × 10-3) = 800 / (8 × 10-10) = 1 × 1012 N/m2.
Ref: University Physics, Chapter 17: Thermal Expansion.