Question

The material of a wire has a density of 1.4 g/cm${}^3$. If it is not wetted by a liquid of surface tension 44 dyne/cm, then the maximum radius of the wire which can float on the surface of liquid is :

• A. $\frac{10}{28}cm$
• B. $\frac{10}{14}cm$
• C. $\frac{10}{7}mm$
• D. 0.7 cm

Answer 1

The correct option is C $\frac{10}{7}mm$

$2Tl=\pi r^{2}Id\times g$
$r=\sqrt{\left(\frac{2T}{\pi dg}\right)}=\sqrt{\frac{2\times 44\times 7}{22\times 1.4\times 980}}$
$=\frac{1}{7}cm=\frac{10}{7}mm$