Unit of surface tension is: [PMT/NEET-2004]
a. N m$^{-1}$
b. N m$^{-2}$
c. N$^2$ m$^{-1}$
d. N m$^{-3}$

Answer: a. N m$^{-1}$

Solution:

Surface tension $T$ is defined as force per unit length along the liquid surface:

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

• Force has unit: $N$
• Length has unit: $m$

So,
$
[T] = \frac{N}{m} = N \, m^{-1}
$

Therefore, the unit of surface tension is newton per metre (N m⁻¹).