Question

A ring is cut from a platinum tube having 10 cm internal and 11 cm external diameter. it is supported horizontally from a pan of the balance so that it comes in contact with water in a glass vessel. what is the surface tension of water if an extra, $4,752g_m$ wt is required to pull it away from water? (g = $10m{s}^{-}2$)

• A. $7.2\times {10}^{-4}N/m$
• B. $72N/m$
• C. $14.4\times {10}^{-}2N/m$
• D. $144N/m$

Answer 1

The correct option is A $7.2\times {10}^{-4}N/m$

Internal diameter = $10cm$

External diameter = $11cm$

extra mass = $4,752gmwt$

We know that force due to surface tension along the Internal and external circumference of platinum

tube = weight

$\Rightarrow T\pi \left(\text{internal diameter+External diameter}\right)=mg$

$\Rightarrow T\pi (10+11)=4.752\times 1000cm/s^2$

$\Rightarrow T=\frac{4752\times {10}^3}{3.14\times 21}=72.0625$ dyne/cm

$=72N/m$

$\therefore$ Hence the tension is found to be $72N/m$.