Q. Two wires A and B made of same material and having their lengths in the ratio 6 : 1 are connected in series. The potential difference across the wires are 3V and 2V respectively. If r* _{A}* and r

*are the radii of A and B respectively, then r*

_{B}*/r*

_{B}*is*

_{A }(a) 1/4

(b) 1/2

(c) 1

(d) 2

Ans: (b)

$ \displaystyle \frac{3}{R_A} = \frac{2}{R_B} $

$ \displaystyle 2R_A = 3R_B $

$\displaystyle 2(\rho \frac{l_A}{\pi r_A^2})= 3(\rho \frac{l_B}{\pi r_B^2}) $

$ \displaystyle \frac{2}{3}\frac{l_A}{l_B} = \frac{r_A^2}{r_B^2} $