Question

Force required to pull a rectangular plate of length $2\text{cm}$ and breadth $3\text{cm}$ from water surface for which surface tension is $75\text{dyne/cm}$ is

• A. $200\text{dyne}$
• B. $750\text{dyne}$
• C. $800\text{dyne}$
• D. $600\text{dyne}$

Answer 1

The correct option is B $750\text{dyne}$

Given:
$T=75\text{dyne/cm}$
$L=2\text{cm}$
$B=3\text{cm}$
$\therefore$ Considered length for surface tension is $2(L+B)\text{cm}$
$\Rightarrow l=2(2+3)\text{cm}$
$\Rightarrow l=10\text{cm}$
Also,
$T=\frac{F}{l}$
$\Rightarrow F=T\times l$
$\Rightarrow F=(75\times 10)\text{dyne}$
$\Rightarrow F=750\text{dyne}$