Question

If the value of surface tension of a liquid is $70$ dynes / cm, then its value in $N / m$ will be :

• A. $7 \times 10^{3} N / m$
• B. $7 \times 10^{2} N / m$
• C. $7 \times 10^{-2} N / m$
• D. $70 \,N / m$

Answer 1

Answer: (C)

The unit dynes/cm is $CGS$ system of unit.
The CGS unit of force is dyne and $SI $ unit is Newton.
Also there are $10^{5}$ dynes in one newton and $100\, cm$ in $1 \,m$.
$\therefore \frac{70 \text { dynes }}{ cm }=\frac{70 \times 10^{-5}}{10^{-2}}$
$=7 \times 10^{-2} \,N / m$