Question

Given below are two statements, one is labelled as Assertion(A) and other one labelled as Reason(R).
Assertion (A): Steel is used in the construction of buildings and bridges.
Reason (R): Steel is more elastic and its elastic limit is high.

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A).
• B. Both (A) and (R) are correct but (R) is NOT the correct explanation of (A).
• C. (A) is correct but (R) is incorrect.
• D. (A) is incorrect but (R) is correct.
• E. Both A and R are not correct

Hint:

In Physics, remember: Elasticity $\neq$ Stretchiness. A material is "more elastic" if it offers more resistance to being deformed and returns to its shape more effectively. This is why steel is technically more elastic than rubber! For Assertion-Reason questions, check both statements individually first, then examine if the reason logically explains the assertion.

Answer 1

The Correct Option is A

Concept: In physics, elasticity refers to a material's ability to return to its original shape after a deforming force is removed. Young's Modulus measures this property — higher modulus indicates greater elasticity. The elastic limit is the maximum stress a material can withstand without permanent deformation.
Step 1: Evaluate Assertion (A). Steel is indeed a primary material for large-scale construction like buildings and bridges because it can withstand heavy loads without permanent deformation. Assertion (A) is correct.

Step 2: Evaluate Reason (R). Contrary to common language where "elastic" means "stretchy" (like rubber), in physics, steel is more elastic than rubber because it requires a much larger force to produce permanent change. Steel has a very high Young's Modulus and a high elastic limit, meaning it can handle extreme stress and still return to its original form. Reason (R) is correct.

Step 3: Establish the relationship between (A) and (R). The reason why steel is used in bridges and buildings is specifically because its high elastic limit allows it to support massive weight, wind loads, and seismic forces without breaking or permanently bending. The high elasticity ensures structural integrity under stress. Thus, (R) correctly explains (A).