Q.

A parallel plate capacitor has capacitance C, when there is vacuum within the parallel plates. A sheet having thickness (1/3)rd of the separation between the plates and relative permittivity K is introduced between the plates. The new capacitance of the system is :          [2026]

1 CK2+K  
2 3CK2(2K+1)2  
3 3KC2K+1  
4 4KC3K-1  

Ans.

(3)

C1=3Aε02d           C2=3Aε0×Kd

C1=32C               C2=3KC

Ceq =C1C2C1+C2=32C×3KC32C+3KC

Ceq =92KC232C(2K+1)=3KC2K+1