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JEE Main 2024 (31 Jan, Shift 1) · Dielectrics

Dielectrics question from JEE Main 2024 (31 Jan, Shift 1)

Q41JEE Main 2024 · 31 JAN · SHIFT 1Medium

Dielectrics

A parallel plate capacitor with plate separation 5 mm5\text{ mm} is charged up by a battery. It is found that on introducing a dielectric sheet of thickness 2 mm2\text{ mm}, while keeping the battery connections intact, the capacitor draws 25%25\% more charge from the battery than before. The dielectric constant of the sheet is _________.

Numerical answer type. Work it out, then open the answer.

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Answer: 2

  1. Battery connected, Q∝CQ\propto C, so C′=1.25CC'=1.25C.
  2. C′=ϵ0Ad−t+tKC'=\frac{\epsilon_0A}{d-t+\frac{t}{K}} with d=5d=5 mm, t=2t=2 mm.
  3. 53+2K=1.25⇒3+2K=4\frac{5}{3+\frac{2}{K}}=1.25 \Rightarrow 3+\frac{2}{K}=4
  4. K=2K=2
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