A copper wire of initial length L and radius r has resistance R0. It is stretched uniformly so that its length becomes 3L. The stretching is done without any loss of material and the temperature remains constant.
(i) Express the new radius r′ in terms of r.
(ii) Show that the new resistance R′ is 9R0.
(iii) If R0=4Ω, calculate the value of R′ after stretching.