When a viscous liquid is flowing through a horizontal capillary tube. The flow is laminar, difference in pressure between the ends of the pipe is $\Delta p$ and the discharge is found to be Q. When two such identical tubes are connected in series , what should be the difference in pressure between its ends if the discharge through it is 2Q?

• A

  8 $\left(\mathrm{\Delta P}\right)$

• B

  $\left(\mathrm{\Delta P}\right)$

• C

  2 $\left(\mathrm{\Delta P}\right)$

• D

  4 $\left(\mathrm{\Delta P}\right)$