Q.

A parallel-plate capacitor of area A, plate separation d and capacitance C is filled with four dielectric materials having dielectric constants k1,k2,k3, and k4 as shown in the figure. If a single dielectric material is to be used to have the same capacitance C in this capacitor, then its dielectric constant k is given by                  [2016]


 

1

k=k1+k2+k3+3k4

 

2

k=23(k1+k2+k3)+2k4

 

3

2k=3k1+k2+k3+1k4

 

4

1k=1k1+1k2+1k3+32k4

 


Ans.

(3)

Here, C1=2ε0k1A3d,  C2=2ε0k2A3d

C3=2ε0k3A3d,  C4=2ε0k4Ad

Given system of C1,C2,C3 and C4 can be simplified as

   1CAB=1C1+C2+C3+1C4

Suppose, CAB=kε0Ad

1(kε0Ad)=12ε0A3d(k1+k2+k3)+12ε0Adk4

1k=32(k1+k2+k3)+12k4        2k=3k1+k2+k3+1k4