Two capillary tubes A and B are arranged in parallel. A liquid flows through these capillary tubes under the same pressure head. Both the tubes have a same length. The radii of A and B are r and $\large\frac{r}{2}$ respectively. If the rate of flow of liquid through A is $8\: cm^3/s$ , then the rate of flow through the combination of A and B is

Question

$\begin {array} {1 1} (1)\;8.0\: cm^3/s & \quad (2)\;8.5 cm^3/s \\ (3)\;12.75 cm^3/s & \quad (4)\;16 cm^3/s \end {array}$