Question

Assertion: A large force is required to draw apart normally two glass plates enclosing a thin water film. Reason: Surface tension of water hold the glass plates together.

Assertion: A small drop of mercury is spherical, but bigger drops are oval in shape. Reason: Surface tension of liquid decreases with increase in size of the drop.

Assertion: The shape of a liquid drop is spherical. Reason: The pressure inside the drop is greater than that of outside.

The property due to which the free surface of liquid tends to have minimum surface area and behaves like a stretched membrane is called surface tension. It is a force per unit length acting in the plane of interface between the liquid and the bounding surface i.e., S = F/L, where F = force acting on either side of imaginary line on surface and L = length of imaginary line. Surface tension decreases with rise in temperature. Highly soluble impurities increases surface tension and sparingly soluble impurities decreases surface tension.