Question

A wire ring of diameter 20cm is gently
lowered on a liquid surface so that its
plane is parallel to the surface and then
pulled up. The extra force applied is
0.084N. The surface tension of the
liquid is

Answer 1

We have,

Diameter of wire ring = 20 $cm$

∴ Radius of wire ring = $r$ = 10 $cm$

And, Extra force applied = 0.084 $N$

∴ The surface tension of the liquid can be derived by using the following formula;

$2$ × $2\pi r$ × σ = 0.084 × $10^5$  

⇒ σ = (0.084 × $10^5$) ÷ ($2$ × $2\pi r$)

⇒ σ = 8400 ÷ {2 × 2 × $\frac{22}{7}$ × 10}   $dynecm^-^1$

⇒ σ = $210$ ÷ $\frac{22}{7}$  $dynecm^-^1$

⇒  σ = [66.8789]  $dynecm^-^1$ = 67  

Ans) Surface tension of the liquid = 67  $dynecm^-^1$