In geometry, a spherical shell is a generalization of an annulus to three dimensions. It is the region of a ball between two concentric spheres of differing radii.^{[1]}
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What is a Spherical Shell?

What is Concept of Spherical Shell .

Gravitation Part 5  Field due to Hollow/thin Spherical Shell [English & Hindi]
Transcription
Volume
The volume of a spherical shell is the difference between the enclosed volume of the outer sphere and the enclosed volume of the inner sphere:
where r is the radius of the inner sphere and R is the radius of the outer sphere.
An approximation for the volume of a thin spherical shell is the surface area of the inner sphere multiplied by the thickness t of the shell:^{[2]}
when t is very small compared to r ().
See also
References
 ^ W., Weisstein, Eric. "Spherical Shell". mathworld.wolfram.com. Wolfram Research, Inc. Archived from the original on 2 August 2016. Retrieved 7 January 2017. CS1 maint: discouraged parameter (link)
 ^ Znamenski, Andrey Varlamov, Lev Aslamazov; scientific editor, A.A. Abrikosov, Jr. ; translators, A.A. Abrikosov, Jr., J. Vydryg, & D. (2012). The wonders of physics (3rd ed.). Singapore: World Scientific. p. 78. ISBN 9789814374156. Archived from the original on 20 December 2017. Retrieved 7 January 2017. CS1 maint: discouraged parameter (link)