Question

A wire $10cm$ long is placed horizontally on the surface of water and is gently pulled up with a force of $1.456\times {10}^{-2}N$ to keep the wire in equilibrium. What is the surface tension of water -

• A. $0.0728N/m$
• B. $-0.072N/m$
• C. $-728N/m$
• D. $728N/m$

Answer 1

The correct option is A $0.0728N/m$

The water film has two surfaces :- $T=\left(F/2l\right)$

$T=(1.456\times {10}^{-2})/(2\times 10\times {10}^{-2})=0.0728N/m$