Calculating resistivity of a gold ring?

Using the resistance equation .. R = ρL / A .. .. ρ = resistivity

R = V/i = 8.30^-3V / 18.0A = 4.60^-4 Ω

Length L = 2πr = 2π x 1.0^-2m = 0.063 m

Section area A = 0.003m x 0.005m = 1.50^-5 m²

ρ = RA / L = 4.60^-4 Ω x 1.50^-5 m² / 0.063 m .. .. ►ρ = 1.10^-7 Ωm

R = resistance , Ω

ρ = Resistivity, Ωm,

L = length, m,

A = area of cross section, m².

Rectangle length, L = 2(3+0.5) X 10 ‾³m = 7 X 10 ‾³m.

Area (cr.s.), A = πr² = π(10 ‾⁴)m²

R = ρ L/A,

R = V/I = 0.0083/18 = 4.61 X 10 ‾⁴Ω

= ρ[7 X 10 ‾³/π(10 ‾⁴] = (70/π)ρ Ωm.

ρ = 4.61 X 10 ‾⁴[π/70] = 20.7 milli Ωm.

It depends where the voltage is applied:

between top face and bottom face

or

between inside face and outside face

or

something else