Question

A wire of resistance 80 ohm is melted and recast to wire of radius 2r find new resistance

Answer 1

R = rho*l/A =rho*l*A/A*A=rho*V/A^2
Its mean R is universally promotional to A^2
Hence A'/A= 4
So R'= *R/(4*4)=80/16=5 ohm