A wire of `3 Omega` resistance and `10 cm` length is stretched to `30 cm` length. Assuming that it has uniform cross-section, what will be its new resistance ?

Explanation

When the length of the wire becomes three times (from 10 cm and 30 cm), its area of cross-section is reduced from A to `A//3`. Therefore, new resistance, `R' = rho ((3 l))/((A//3)) = 9 (rho l)/(A) = 9 R = 9(3 Omega) = 27 Omega`.