Question

Resistance of a wire is 9 ohm if length of wire is tripled by stretching it.find its new resistance.

Answer 1

R=rhoL/A....1
That is ...R is directly proportional to L
Since now the length has become 3 times that means L can be substituted as 3L
So new resistance R`=rho(3L)/A......or R`=3 rho L / A.....2
Comparing 1 and 2
R`=3R
R` ie new resistance will be 3×9=27ohm