(a) A copper wire of original length L and radius r is stretched uniformly so that its length becomes 1.5L. Assuming that the volume of the wire remains constant during stretching, obtain an expression for the new radius r′.
(b) On the basis of the result in part (a), derive an expression for the new resistance R′ of the wire in terms of its original resistance R.
(c) If the original resistance was 2.0Ω, calculate the numerical value of the new resistance after stretching.