Question

A $10\text{cm}$ long wire is placed horizontal on the surface of water and is gently pulled up with a force of $2\times {10}^{-2}\text{N}$ to keep the wire in equilibrium. The surface tension (in ${\text{Nm}}^{-1}$) of water is

• A. $0.1$
• B. $0.2$
• C. $0.001$
• D. $0.002$

Answer 1

The correct option is A $0.1$

Surface tension acting on the long wire is balanced by the upward applied force.
$\therefore T=\frac{F}{2l}$ (Surface tension working on either sides of the length of the wire)
$\Rightarrow T=\frac{2\times {10}^{-2}}{2\times 10\times {10}^{-2}}=0.1{\text{Nm}}^{-1}$