Q.

A parallel plate capacitor with plate separation 5 mm is charged by a battery. On introducing a mica sheet of 2 mm and maintaining the connections of the plates with the terminals of the battery, it is found that it draws 25% more charge from the battery. The dielectric constant of mica is __________.  [2026]

1 2.0  
2 1.5  
3 1.0  
4 2.5  

Ans.

(1)

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ceq=C1C2C1+C2=ε0A3×Kε0A2ε0A3+Kε0A2

ceq=(ε0A)2(K6)ε0A(2+3K6)Ceq=Kε0A2+3K

1.25×ε0A5=Kε0A2+3K0.25(2+3K)=K

         2+3K=4KK=2