Copper wire has resistance R. if the wire is made in a circular shape, find resistance between two diametrical opposite point in terms of original resistance.

The copper wire is bent in a circle. When two diametrically opposite points are considered, we can imagine that, two resistances of value R/2 are connected in parallel.

 

Thus, the resistance between these two points is;

1/R' = 2/R + 2/R = 4/R

 

Thus, we have

R' = R/4