Question

Spring index is given as 15 and mean diameter of coil is 90 mm. Diameter of wire is __________

(a) 6 mm

(b) 5 mm

(c) 7 mm

(d) 8 mm

The question was posed to me in an online interview.

This interesting question is from Construction of Helical Springs in section Curves used in Engineering Practice of Engineering Drawing

Answer 1

Right option is (a) 6 mm

To explain I would say: The ratio of a mean diameter of the coil to diameter of wire gives spring index. 90 mm / diameter of wire = 15, diameter of wire = 90 mm / 15 = 6 mm. This spring index sometimes gives the strength to spring and used in calculating stress through it.