NEET 2020 Physics Young's Modulus MCQ Question
A wire of length L, area of cross section A is hanging from a fixed support. The length of the wire changes to L₁ when mass M is suspended from its free end. The expression for Young's modulus is :
MgL / AL₁
MgL / A(L₁ − L)
MgL₁ / AL
Mg(L₁ − L) / AL
Correct Answer
Detailed Explanation
Young's modulus Y = Stress/Strain = (F/A)/(ΔL/L) = (F × L)/(A × ΔL). Here F = Mg and ΔL = L₁ − L. Therefore Y = MgL / [A(L₁ − L)]. The original explanation incorrectly wrote Mg(L₁−L)/(AL), which inverts the strain. The correct answer is B.
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