Q. Two capillary of length L and 2L and of radii R and 2R are connected in series. The net rate of flow of fluid through them will be (given rate of the flow through single capillary, X=$\ \frac{\pi pR^{4}}{8ɳL}$)

A) $\frac{8}{9}X$
B) $\frac{9}{8}X$
C) $\frac{5}{7}X$
D) $\frac{7}{5}X$
Explanation

(a) $Fluid\ resistance\ is\ given\ by\ \ \ \ \ R = \frac{8ɳL}{{\pi r}^{4}}$
When two capillary tubes of same size are joined in parallel, then equivalent fluid resistance is
$R_{eq} = R_{1} + R_{2} = \frac{8ɳL}{{\pi R}^{4}} + \frac{8ɳ \times 2L}{\pi(2R)^{4}}$
Equivalent resistance becomes$\ \ \ \frac{9}{8}$ times so,$\ $
$rate\ of\ flow\ will\ be\frac{8}{9}X.$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.