Question

When one end of the capillary is dipped in water, the height of water column is ${}^{\prime }{h}^{\prime }$. The upward force of $105$ dyne due to surface tension balanced by the force due to the weight of water column. The inner circumference of the capillary is
(Surface tension of water $=7\times {10}^{-2}N/m)$

• A. $1.5cm$
• B. $2cm$
• C. $2.5cm$
• D. $3cm$

Answer 1

The correct option is A $1.5cm$

Upward force acting $F=105$ dyne $=105\times {10}^{-5}$ $N$

Surface tension of water $T=7\times {10}^{-2}N/m$

Surface tension acts at the circumference $C$ of the capillary tube.

.$\therefore$ $F=CT$

Or $105\times {10}^{-5}=C\times 7\times {10}^{-2}$

Or $C=15\times {10}^{-3}m$

$⟹$ $C=15\times {10}^{-1}cm=1.5cm$