NEET 2016 Phase 2 · PhysicsSurface energyPrevious Year Question
A rectangular film of liquid is extended from (4 cm × 2 cm) to (5 cm × 4 cm). If the work done is 3 × 10⁻⁴ J, the value of the surface tension of the liquid is:
Answer: (B) 0.125 N m⁻¹. A film has TWO surfaces.
- A.0.250 N m⁻¹
- B.0.125 N m⁻¹✓
- C.0.2 N m⁻¹
- D.8.0 N m⁻¹
Correct Answer
(B) 0.125 N m⁻¹
Solution & Explanation
A film has TWO surfaces. ΔA = (5×4 − 4×2) = 12 cm² = 12 × 10⁻⁴ m². W = T·(2·ΔA) ⇒ T = W/(2ΔA) = 3×10⁻⁴ / (2 × 12×10⁻⁴) = 0.125 N m⁻¹.
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