A capacitor has capacitance $C_0$ when there is no dielectric between it's plates. 2 slabs of dielectric…

A capacitor has capacitance $C_0$ when there is no dielectric between it's plates. 2 slabs of dielectric constant $K_1, K_2$ respectively with area equal to area of plates but thickness half of the distance between the plates are placed in between the plates. Then the new capacitance is
  1. $C_0\left(K_1+K_2\right)$
  2. $C_0\left(\frac{K_1 K_2}{K_1+K_2}\right)$
  3. $C_0\left(\frac{K_1+K_2}{K_1 K_2}\right)$
  4. $2 C_0\left(\frac{K_1 K_2}{K_1+K_2}\right)$

Solution

Initial capacitance of capacitor, $C_0=\frac{\varepsilon_0 A}{d}$
Now, capacitor is filled with two dielectrics each slab has area $A$ and distance $d / 2$ as shown
Above arrangement is a series combination of two capacitors as shown
so, capacity of above arrangement is $\frac{1}{C_{\mathrm{eq}}}=\frac{1}{C_1}+\frac{1}{C_2}$ $\begin{aligned} & =\frac{1}{\frac{\varepsilon_0 K_1 A}{(d / 2)}}+\frac{1}{\varepsilon_0 K_2 A /(d / 2)} \\ & =\frac{d}{2 \varepsilon_0 A}\left[\frac{1}{K_1}+\frac{1}{K_2}\right]\end{aligned}$ $\begin{aligned} & \Rightarrow \frac{1}{C_{\mathrm{eq}}}=\frac{d}{2 \varepsilon_0 A}\left[\frac{K_1+K_2}{K_1 K_2}\right] \\ & \Rightarrow C_{\mathrm{eq}}=\frac{2 \varepsilon_0 A}{d}\left[\frac{K_1 K_2}{K_1+K_2}\right] \\ & \Rightarrow C_{\mathrm{eq}}=2 C_0\left(\frac{K_1 K_2}{K_1+K_2}\right)\end{aligned}$

Asked in: AP EAMCET 2022 (07 Jul Shift 1)

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