Question

The porosity of intermediate packing factor is given by ______

(a) n = 1-[1/(6*(1-cosα)*( √(1-2cosα) )]

(b) n = (1-cosα)*( √(1+2cosα) )

(c) n = 1-[π/(6*(1-cosα)*(√(1-2cosα))]

(d) n = 6*(1-cosα)*(√(1-2cosα))

The question was posed to me during an interview for a job.

My doubt is from Packing of Uniform Spheres in section Preliminary Definitions and Relationships of Geotechnical Engineering I

Answer 1

Right answer is (c) n = 1-[π/(6*(1-cosα)*(√(1-2cosα))]

Explanation: The formula was given by Slichter. In an intermediate packing, the centres of any 8 spheres, originally arranged in a cubic packing form the corners of the rhombohedron, with an acute face angle α.