A uniform wire resistance `100(Omega)`is melted and recast in a wire of length double that of the original . What would be the resistance of the wire?

Explanation

`l = 2l Volume of wire remains constant
Ai = A' I' `
` rArr Ai = A' xx 2i `
` rArr A' = A/2 `
rho rArr Specific resistance `
` R = rhol/A' `
` R_1= rhol/A = 100 Omega `
` = (rho 2l/A/2) = (4rhol /A) = 4R`
` = 4 xx 100 Omega = 400Omega ` .