Q.

A capacitor has air as dielectric medium and two conducting plates of area 12 cm2 and they are 0.6 cm apart. When a slab of dielectric having area 12 cm2 and 0.6 cm thickness is inserted between the plates, one of the conducting plates has to be moved by 0.2 cm to keep the capacitance same as in previous case. The dielectric constant of the slab is

(Given ε0=8.834×10-12 F/m)         [2024]

1 1  
2 0.66  
3 1.33  
4 1.50  

Ans.

(4)

Parallel plate capacitance, C=ϵoAd1

For partially filled capacity, C=ϵoA(d2-t+tk)

For case (i) C1=ϵoA0.6, For case (ii) C2=ϵoA0.8-0.6+0.6K

Now C1=C2,ϵoA0.6=ϵoA0.2+0.6K,

0.6=0.2+0.6KK=32