Question

With the increase in temperature, the angle of contact
A- increase
B- decreases
C- Remains constant
D- first increases and then decreases

Answer 1

Hint: When the liquid is placed in contact with some solid, then the angle formed between the two surfaces and the tangent to the free surface of the liquid at the point of contact, measured from inside the liquid is called the angle of contact.

Complete step by step answer:
The angle of contact is constant for a given liquid-solid pair. So, let us find out the dependence of the angle of contact on different factors. When the angle of contact is acute then the liquid is said to wet the surface. If the angle of contact is more than acute then they alter the values of the angle of contact.
Talking about the temperature dependence, the angle of contact decreases with the increase in the temperature. as the temperature increases, the angle of contact decreases due to decreased cohesive force.

So, the correct answer is “Option B”.

Note:
The presence of impurities also affects the temperature dependence of the angle of contact. For a liquid which completely wets all the surface in which it is in contact, the angle of contact is equal to zero. Also, if the size of the drop is quite small then gravitational potential energy for that is too small and thus it affects can be neglected. For large drop sizes, gravitational potential energy is taken into account. Presence of impurities like petrol makes the shape concave.