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JEE Advanced 2015Paper 2
Exam
JEE Advanced
Year
2015
Paper
Paper 2
Subject
Physics
Chapter
Capacitance

JEE Advanced 2015 · Paper 2 · Physics · Capacitance

A parallel plate capacitor having plates of area S and plate...

A parallel plate capacitor having plates of area SS and plate separation dd , has capacitance C1{C}_{1} in air. When two dielectrics of different relative permittivities ( ε1=2{ε}_{1} = 2 and ε2=4{ε}_{2} = 4 ) are introduced between the two plates as shown in the figure, the capacitance becomes C2{C}_{2} . The ratio C2C1\dfrac{{C}_{2}}{{C}_{1}} is

A parallel plate capacitor having plates of area S and plate separation d , has capacitance C _ 1 in air. When two

Options

  1. A65\dfrac{6}{5}
  2. B53\dfrac{5}{3}
  3. C75\dfrac{7}{5}
  4. D73\dfrac{7}{3}

Correct answer

D. 73\dfrac{7}{3}

Step-by-step solution

5ϵ0d=C1\dfrac{5{ϵ}_{0}}{d} = {C}_{1}
In new setup we have 3 different setups
i. 52,d2,ϵ1\dfrac{5}{2}, \dfrac{d}{2}, {ϵ}_{1}
C′=52ϵ1ϵ0d2=2C1{C}^{′} = \dfrac{\dfrac{5}{2}{ϵ}_{1}{ϵ}_{0}}{\dfrac{d}{2}} = 2{C}_{1}
ii. 52,d2,ϵ2\dfrac{5}{2}, \dfrac{d}{2}, {ϵ}_{2}
C′′=52ϵ2ϵ0d2=4C1{C}^{′′} = \dfrac{\dfrac{5}{2}{ϵ}_{2}{ϵ}_{0}}{\dfrac{d}{2}} = 4{C}_{1}
iii. 52,d,ϵ1\dfrac{5}{2}, d, {ϵ}_{1}
C′′′=52ϵ1ϵ0d=C1{C}^{′′′} = \dfrac{\dfrac{5}{2}{ϵ}_{1}{ϵ}_{0}}{d} = {C}_{1}

A parallel plate capacitor having plates of area S and plate separation d , has capacitance C _ 1 in air. When two
C2=(12C1+14C1)−1+C1=146C1=73C1{C}_{2} = {\left(\dfrac{1}{2{C}_{1}} + \dfrac{1}{4{C}_{1}}\right)}^{- 1} + {C}_{1} = \dfrac{14}{6}{C}_{1} = \dfrac{7}{3}{C}_{1}
∴C2C1=73∴ \dfrac{{C}_{2}}{{C}_{1}} = \dfrac{7}{3}
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