Surface Tension - Practice Questions & MCQ

Surface tension is the elastic tendency of a fluid surface which makes it acquire the least surface area.

If we draw an imaginary line on the free surface of the liquid as shown in the below figure.

Then Surface tension of a liquid is measured by the force acting per unit

length on either side of an imaginary line.

So  Surface tension of a liquid  is given by 

$$
T=\frac{F}{l}
$$

Where

$$
F \rightarrow \text { force }
$$

$l \rightarrow$ imaginary length
The direction of this force is perpendicular to the line and tangential to the free surface of the liquid.
- It depends only on the nature of liquid and is independent of the area of surface or length of the imaginary line considered.
- It is a scalar quantity.
- Unit of Surface Tension-

$$
\begin{aligned}
& \frac{N}{m}-i n \text { S.I. Unit } \\
& \frac{d y n e}{c m}-i n \text { c.g.s. Unit }
\end{aligned}
$$

- Dimension- $M T^{-2}$

• Example-

     Raindrops are spherical in shape because each drop tends to acquire minimum surface area due to surface tension, and for a  given volume, the surface area of the sphere is minimum.

• The surface tension of liquid decreases with the rise of temperature.