Q.30) The plates of alparallel plate capacitor are separated by $d$. Two slabs of different dielectric constant $K_1$ and $K_2$ with thickness $\frac{3}{8} d$ and $\frac{d}{2}$, respectively arerinserted in the capacitor. Due to this, thercapacitance becomes two times larger that when there is nothing between the plates.
If $K_1=1.25 K_2$, the value of $K_1$ is :
A)
1.33
B) 2.66
C) 2.33
D) 1.60
Given $C=2 C_0$, so:
$$
\frac{3}{8 K_1}+\frac{1}{2 K_2}+\frac{1}{8}=\frac{1}{2}
$$
Substitute $K_1=1.25 K_2 \Rightarrow K_2=\frac{K_1}{1.25}$, solve:
$$
\frac{3}{K_1}+\frac{4 \cdot 1.25}{K_1}=3 \Rightarrow \frac{8}{K_1}=3 \Rightarrow K_1=\frac{8}{3} \approx 2.66
$$
Answer: (2) 2.66