Correct Answer - Option 2 : Load required to produce unit deflection
Explanation:
Spring constant / Stiffness of a spring (k):
Load required to produce unit deflection.
\(k = \frac{P}{\delta }\)
where P = Load & δ = Deflection.
Deflection of spring in terms of active turns:
\(\delta = \frac{{8P{D^3}N}}{{G{d^4}}}\)
\(∴ k = \frac{P}{{\frac{{8P{D^3}N}}{{G{d^4}}}}} ⇒ \frac{{G{d^4}}}{{8{D^3}N}}\)
where D = Diameter of the spring coil, d = Diameter of spring wire, N = No. of active turns, and G = Modulus of Rigidity.
