Question

Surface tension of water is$0.072N/m$. The excess pressure inside a water drop of a diameter $1.2mm$ is:

• A. $240N/m^2$
• B. $24N/m^2$
• C. $0.06N/m^2$
• D. $60N/m^2$

Answer 1

The correct option is B

$24N/m^2$

Explanation for correct option

Step 1. Given data

1. Surface tension$\left(S\right)$ of water is $0.072N/m$
2. Diameter of water drop$\left(D\right)=1.2mm=0.012m$

Step 2. Formula used

1. Radius$\left(r\right)=\frac{D}{2}$
2. $∆P=\frac{2S}{r}$

Where $r$ is the radius , $D$ is the diameter, $S$ is the surface tension, $∆P$ is the exerted pressure

Step 3. Find the exerted pressure inside the water drop

$S=0.072N/m$

$r=\frac{0.012}{2}=0.006m$

$$\begin{gathered} ∆P=\frac{2S}{r} \\ =\frac{2\times 0.072}{0.006} \\ =24N/m^2 \end{gathered}$$

Hence, Option B is correct