tregor kasto yaar timi ta jhann tyesto ramro sanga expain gare. la hera. let me try differently then. your only problem is that you somehow are stuck with the idea of rho being a constant haina? ok here we go since you assumed rho to be constant b/c temp is constant. similarly one can assume the area is constant and length is constant for a given uniform wire-like conductor, for e.g. then lets assume our area is constant b/c we have a uniform area through out. we can do that can we not? now, R = rho*L/A since rho and area are both constant we say K = rho/A R = K*L so it is now proportional to length. haina ta. you cannot ignore dimensions even if it is that os something assumed to be constant. if you are still not convinced you really need to talk to a physics instructor. have fun and bring more of this in future