Two wires A and B of the same material have their lengths in the ratio of 1:2 and their diameters in the ratio of 2:1. If they are stretched with the same force, the ratio of the increase in the length of A to that of B will be
1:8
Here, l1=FL1πr21Y and l2=FL2πr22Y.
Therefore, l1l2=L1L2×(r2r1)2
Given that, L2=2L1 and r2=r12
Thus, l1l2=12×1(2)2=18.
Hence, the correct choice is (c).