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Question: Answered & Verified by Expert
If a slab of insulating material (conceptual). $4 \times 10^{-3} \mathrm{~m}$ thick is introduced between the plates of a parallel plate capacitor, the separation between the plates has to be increased by $3.5 \times 10^{-3} \mathrm{~m}$ to restore the capacity to original value. The dielectric constant of the material will be
PhysicsCapacitanceKCETKCET 2021
Options:
  • A 6
  • B 8
  • C 10
  • D 12
Solution:
2446 Upvotes Verified Answer
The correct answer is: 8
Let $t$ be the thickness of the dielectric slab and $K$ is the dielectric constant.
So, the increase in the distance of separation between the plates due to dielectric is given as
$\begin{aligned}
x &=t-\frac{t}{K} \\
&=t\left(1-\frac{1}{k}\right)
\end{aligned}$
Given, $x=3.5 \times 10^{-3} \mathrm{~m}, t=4 \times 10^{-3} \mathrm{~m}$
Substituting the given values in the above equation, we get
$1-\frac{1}{k}=\frac{x}{t}=\frac{3.5 \times 10^{-3}}{4 \times 10^{-3}}=\frac{3.5}{4}$
or
$\frac{1}{k}=1-\frac{3.5}{4}=\frac{0.5}{4}$
or
$k=8$

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