Question

Water proofing agent changes the angle of contact:

• A. from an obtuse to acute value
• B. from an acute to obtuse value
• C. from obtuse to $\frac{\pi }{2}$
• D. from acute to $\frac{\pi }{2}$

Answer 1

The correct option is B from an acute to obtuse value

The purpose of water proofing agent is to alter the surface of a solid such that it starts repelling water.

Initially, the surface was getting wet by water as water tends to spread on the surface, because contact angle is acute $(\theta <{90}^{\circ })$

If the solid surface (eg: clothes) are sprayed with waterproofing agent, then it changes the angle of contact from acute to obtuse.


Hence, water tends to be repelled from the surface and beads up on the surface and does not easily penetrate the clothing.