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MHT CET 2021 (20 Sep, Shift 2) · Dielectrics

Dielectrics question from MHT CET 2021 (20 Sep, Shift 2)

Q79MHT CET 2021 · 20 SEP · SHIFT 2Medium

Dielectrics

A parallel plate air capacitor is charged upto 100 V. A plate 2 mm thick is inserted between the plates. Then to maintain the same potential difference, the distance between the plates is increased by 1.6 mm. The dielectric constant of the thick plate is

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Answer: (b)

A slab of thickness $t$ reduces the effective gap by $t\left(1-\frac{1}{K}\right)$ .
To keep $C$ (and $V$ ) the same, the gap must grow by this amount: $t\left(1-\frac{1}{K}\right)=1.6$ mm
$2\left(1-\frac{1}{K}\right)=1.6 \Rightarrow \frac{1}{K}=0.2$
So the answer is (b) $K=5$ .

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