Q.

A parallel plate capacitor is filled equally (half) with two dielectrics of dielectric constant ε1 and ε2, as shown in figures. The distance between the plates is d and area of each plate is A. If capacitance in first configuration and second configuration are C1 and C2 respectively, then C1C2 is          [2025]

1 ε1ε22(ε1+ε2)2  
2 4ε1ε2(ε1+ε2)2  
3 ε1ε2ε1+ε2  
4 ε0(ε1+ε2)2  

Ans.

(2)

C1=ε0Ad2ε1+d2ε2=ε0Ad{1ε2+ε12ε1ε2}

C2=ε0d(ε1A2+ε2A2)=ε0Ad{ε12+ε22}

C1C2=2ε1ε2(ε2+ε1)(ε1+ε2)2=4ε1ε2(ε1+ε2)2