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}cm $
• D. $ 0.7cm $

Answer 1

Answer: (C)

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