Surface tension (T) = (F)/(l) = (γ) = (ΔP)/(Δr)
Excess pressure (ΔP) = (2T)/(r)
Work done (W) = (T) × (ΔA)
E = (γ) × (A)
C = (1/(2T)) × (ρ) × (g) × (r)²
r = (2T)/(ΔP) = (2T)/(ρgh)
l = (γ)/(g) × (ρ)²
T = (h) × (ρ) × (g) × (cosθ)

🪤 The 5 Mistakes That Cost Marks

Not considering the effect of temperature on surface tension
Forgetting to convert units of surface tension from N/m to J/m²
Not using the correct formula for excess pressure
Confusing surface energy with surface tension
Not applying the formula for work done ∈ the correct context

✏️ 3 Solved PYQs

Question 1: What is the surface tension of a liquid if its surface energy is 0.072 J/m²?
Step 1: Recall the formula E = γ × A
Step 2: Since surface energy is given, we can directly equate it to surface tension
Step 3: γ = E/A = 0.072 J/m²
Answer: γ = 0.072 J/m²
Question 2: A drop of water has a diameter of 4 mm. If the surface tension of water is 0.072 N/m, what is the excess pressure inside the drop?
Step 1: Recall the formula ΔP = (2T)/(r)
Step 2: Convert diameter to radius, r = (4 mm)/2 = 2 mm = 0.002 m
Step 3: ΔP = (2 × 0.072 N/m)/(0.002 m) = 72 N/m²
Answer: ΔP = 72 N/m²
Question 3: What is the work done ∈ increasing the surface area of a film from 0.5 m² to 1.5 m² if the surface tension is 0.040 N/m?
Step 1: Recall the formula W = T × ΔA
Step 2: ΔA = (1.5 m²) - (0.5 m²) = 1 m²
Step 3: W = (0.040 N/m) × (1 m²) = 0.040 J
Answer: W = 0.040 J

🧠 The One Thing Most Students Get Wrong

Most students get confused between surface energy and surface tension. Surface energy is the energy per unit area of the surface, while surface tension is the force per unit length of the surface.

👁️ Ayush's Note

To solve problems related to surface tension, always start by identifying the given parameters and the unknown quantity.
Use the formula bank to find the relevant equation and plug ∈ the values.
Make sure to convert units correctly and check the dimensions of the equation.

🔁 Last 5 Minutes Box

Surface tension is a property of the surface of a liquid
It is measured ∈ N/m or J/m²
Excess pressure is the difference ∈ pressure between the inside and outside a bubble or drop
Surface energy is the energy per unit area of the surface
Work done is the product of surface tension and change ∈ surface area

📝 Practice MCQs

1. What is the surface tension of a liquid if its surface energy is 0.072 J/m²?

A) 0.072 N/m

B) 0.072 J/m²

C) 0.072 Pa

D) 0.072 J

Answer: B) 0.072 J/m². Surface energy is equal to surface tension.

2. A drop of water has a diameter of 4 mm. If the surface tension of water is 0.072 N/m, what is the excess pressure inside the drop?

A) 36 N/m²

B) 72 N/m²

C) 144 N/m²

D) 288 N/m²

Answer: B) 72 N/m². Use the formula ΔP = (2T)/(r).

3. What is the work done ∈ increasing the surface area of a film from 0.5 m² to 1.5 m² if the surface tension is 0.040 N/m?

A) 0.020 J

B) 0.040 J

C) 0.060 J

D) 0.080 J

Answer: B) 0.040 J. Use the formula W = T × ΔA.

4. What is the units of surface tension?

A) N/m

B) J/m²

C) Pa

D) Both A and B

Answer: D) Both A and B. Surface tension can be measured ∈ both N/m and J/m².

5. What is the effect of temperature on surface tension?

A) Increases with increase ∈ temperature

B) Decreases with increase ∈ temperature

C) Remains constant with increase ∈ temperature

D) Increases with decrease ∈ temperature

Answer: B) Decreases with increase ∈ temperature. Surface tension decreases with increase ∈ temperature.

⚗️ Chemical Quick Reference (Verified via PubChem)

Compound	Formula	Mol. Weight	Source
water	H2O	18.015 g/mol	PubChem ↗

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📚 Academic References

Content verified against peer-reviewed research:

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This post was curated by Jules, Exam Compass Bot, and edited for accuracy by Ayush.

📚 Related Topics

Continue your revision with these related guides:

Surface tension (T) = (F)/(l) = (γ) = (ΔP)/(Δr)
Excess pressure (ΔP) = (2T)/(r)
Work done (W) = (T) × (ΔA)
E = (γ) × (A)
C = (1/(2T)) × (ρ) × (g) × (r)²
r = (2T)/(ΔP) = (2T)/(ρgh)
l = (γ)/(g) × (ρ)²
T = (h) × (ρ) × (g) × (cosθ)