NEET 2025 · PhysicsDielectricsPrevious Year Question
The plates of a parallel plate capacitor are separated by d. Two slabs of different dielectric constant K1 and K2 with thickness 3d/8 and d/2 respectively are inserted in the capacitor. Due to this, the capacitance becomes two times larger than when there is nothing between the plates. If K1/K2 = 1.25, the value of K1 is:
- A.1.60
- B.1.33
- C.2.66✓
- D.2.33
Correct Answer
(C) 2.66
Solution & Explanation
Answer: (c) Solution: C' = ε₀A / (d - t₁ - t₂ + t₁/K₁ + t₂/K₂) = 2(ε₀A/d). With t₁ = 3d/8, t₂ = d/2: d - 3d/8 - d/2 = d/8, so d/8 + (3d/8)/K₁ + (d/2)/K₂ = d/2. Using K₂ = K₁/1.25 = 0.8K₁: (3/8)/K₁ + (1/2)/(0.8K₁) = 3/8 → (1/K₁)(3/8 + 5/8) = 3/8 → K₁ = 8/3 ≈ 2.66. → option (c).
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