The resistance of a wire is R. When this wire is stretched so that its length becomes double, its cross-sectional area becomes half. What will be the resistance of this stretched wire?

Options

A. `R/2`
B. `R`
C. `2R`
D. `4R`

Answer

D

Explanation

Original resistance of the wire `R = rho . l/A`
Resistance of the stretched wire `R. = rho. (l.)/(A.)`
But 1 = 2 an A ` = A/2`
`:. R. =rho (2l)/(A/2) = (4) rho 1/A =4R`