JEE Advanced2015PhysicsCapacitanceActual
A parallel plate capacitor having plates of area S and plate separation d , has capacitance C 1 in air. When two dielectrics of different relative permittivities ( ε 1 = 2 and ε 2 = 4 ) are introduced between the two plates as shown in the figure, the capacitance becomes C 2 . The ratio C 2 C 1 is
Options
- A6 5
- B5 3
- C7 5
- D7 3
Correct answer
D. 7 3
Step-by-step solution
5 ϵ 0 d = C 1 In new setup we have 3 different setups i. 5 2 , d 2 , ϵ 1 C ′ = 5 2 ϵ 1 ϵ 0 d 2 = 2 C 1 ii. 5 2 , d 2 , ϵ 2 C ′ ′ = 5 2 ϵ 2 ϵ 0 d 2 = 4 C 1 iii. 5 2 , d , ϵ 1 C ′ ′ ′ = 5 2 ϵ 1 ϵ 0 d = C 1 C 2 = 1 2 C 1 + 1 4 C 1 - 1 + C 1 = 14 6 C 1 = 7 3 C 1 ∴ C 2 C 1 = 7 3