For the given solid-liquid pair, | PGMN Solutions

For the given solid-liquid pair,
T1 is the force due to surface tension at liquid-solid interface,
T2 is the force due to surface tension at air-solid interface and
T3 is the force due to surface tension at air-liquid interface

For equilibrium of drop, if (T2 - T1) is less than T3 and cos theta is positive then angle of contact will be**
(A) acute  (B) zero  (C) obtuse  (D) ninety degrees
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🚀 Step-by-Step Solution to Solve This Question 🚀
📌 Chapter: Surface Tension
📌 Topic: Angle of Contact

🔹 Step 1: Introduce the core concept
The angle of contact is the angle formed between the tangent to the liquid surface and the solid surface at the point of contact. It shows whether a liquid spreads over a solid surface or forms a droplet.

🔹 Step 2: Explain how it applies here
The nature of this angle is influenced by the forces due to surface tension acting at three interfaces: between the solid and liquid, between the solid and air, and between the liquid and air. The balance of these forces determines whether the liquid tends to spread or stay compact.

🔹 Step 3: Break down the reasoning step-by-step
Here, the force difference between air-solid and liquid-solid interfaces is said to be less than the force at the air-liquid interface. Also, it is given that the cosine of the angle is positive.
When the cosine of the angle is positive, it means the angle lies between zero and ninety degrees. This occurs when the liquid has a tendency to spread over the solid surface.

🔹 Step 4: Explain the final conceptual conclusion
Since the cosine of the angle is positive and the difference in forces is less than the force at the air-liquid interface, the liquid partially wets the surface and the angle formed is smaller than ninety degrees — which is an acute angle.

✅ Final Answer: (A) acute 🚀🚀 Step-by-Step Solution to Solve This Question 🚀
📌 Chapter: Surface Tension
📌 Topic: Angle of Contact

🔹 Step 1: Introduce the core concept
The angle of contact is the angle formed between the tangent to the liquid surface and the solid surface at the point of contact. It shows whether a liquid spreads over a solid surface or forms a droplet.

🔹 Step 2: Explain how it applies here
The nature of this angle is influenced by the forces due to surface tension acting at three interfaces: between the solid and liquid, between the solid and air, and between the liquid and air. The balance of these forces determines whether the liquid tends to spread or stay compact.

🔹 Step 3: Break down the reasoning step-by-step
Here, the force difference between air-solid and liquid-solid interfaces is said to be less than the force at the air-liquid interface. Also, it is given that the cosine of the angle is positive.
When the cosine of the angle is positive, it means the angle lies between zero and ninety degrees. This occurs when the liquid has a tendency to spread over the solid surface.

🔹 Step 4: Explain the final conceptual conclusion
Since the cosine of the angle is positive and the difference in forces is less than the force at the air-liquid interface, the liquid partially wets the surface and the angle formed is smaller than ninety degrees — which is an acute angle.

✅ Final Answer: (A) acute 🚀
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