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Question: Answered & Verified by Expert
A certain series R-C circuit is formed using  resistance R, a capacitor without dielectric having a capacitance C = 2 F and a battery of emf E = 3 V. The circuit is completed and it is allowed to attain the steady state. After this, at t = 0 half the thickness of the capacitor is filled with a dielectric constant k = 2 as shown in the figure. The system is again allowed to attain a  steady state. What will be the heat generated (in joule) in the capacitor between t = 0 and t = ?

PhysicsElectrostaticsJEE Main
Options:
  • A 3
  • B 5
  • C 2
  • D 6
Solution:
1014 Upvotes Verified Answer
The correct answer is: 3
Initial charge on capacitor = CE

Initial potential energy of capacitor = CE2/2

Now,        C = ε 0 A/d

And new capacitance C = ε 0 A d/2 , in series with = ε 0 K A d/2

     C ' =  2 0    A d in series with  4 0 A d

= ε 0 A d 2 × 4 2 + 4 = 4 ε 0 A 3 d = 4 3 C

    New charge = 4 3 CE

New energy = 1 2 × 4 3 CE 2 = 2 3 CE 2

Now W battery = Δ H + Δ U

E 4 3 CE - CE = Δ H + 2 3 CE 2 - 1 2 CE 2

Δ H = 1 6 CE = 3

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