NEET2026PhysicsChapterActual
Given below are two statements : One is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): When a load is suspended from a vertical helical spring, the volume of the wire used to make the spring remains practically constant. Reason (R): The extension of a helical spring is determined by the shear modulus of its material, and shearing strain does not produce any change in volume. In the
Options
- ABoth (A) and (R) are true and (R) is the correct explanation of (A)
- BBoth (A) and (R) are true but (R) is not the correct explanation of (A)
- C(A) is true but (R) is false
- D(A) is false but (R) is true
Correct answer
A. Both (A) and (R) are true and (R) is the correct explanation of (A)
Step-by-step solution
When a load is suspended from a vertical helical spring, the wire of the spring is subjected to torsional shear stress. The elongation of the spring is primarily due to the twisting of the wire. The spring constant is given by k = G r^4 4 R^3 N , where G is the shear modulus of the material. This shows that the extension of the spring is determined by the shear modulus. Since the deformation is purely due to shear strain, and shear strain involves only a change in shape without any change in volume, the volume of t