A spherical shell is heated. The volume changes according to the equation V_θ = V₀ (1 + γθ). Does the volume refer to the volume enclosed by the shell or the volume of the material making up the shell?

When heated, the volume of a spherical shell varies according to the equation V_θ = V₀ (1 + γθ). As the volume of spherical shell expands with rise of temperature, the volume referred here is volume of the material used to make up the shell. Here, the coefficient of expansion of volume is γ.