When a wire of uniform cross-section a, length l and resistance R is bent into a complete circle, resistance between two of diametrically opposite points will be

When the wire is bent to form a complete circle, then2πr=R⇒r=R2πResistance of each semicircle=πr=πR2π=R2Thus, net resistance in parallel combination of two semicircular resistancesR'=R2 × R2 R2 + R2=R24R  =  R4