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.

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.

A 10 cm long wire is placed horizontally on the surface of water and is gently pulled up with a force of 2 × 10⁻² N to keep the wire in equilibrium. The surface tension in Nm⁻¹ of water

A liquid film is formed over a frame ABCD as shown in figure. Wire CD can slide without friction. The mass to be hung from CD to keep it in equilibrium is