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 rA and rB are the radii of A and B respectively, then rB /rA is
(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} $