Two identical parallel plate capacitors, of capacitance C each, have plates of area A , separated by a…

Two identical parallel plate capacitors, of capacitance C each, have plates of area A, separated by a distance d . The space between the plates of the two capacitors, is filled with three dielectrics, of equal thickness and dielectric constants K1, K2 and K3 . The first capaciitor is filled as shown in figure I, and the second one is filled as shown in figure II.
If these two modified capacitors are charged by the same potential V , the ratio of the energy stored in the two, would be (E1 refers to capacitor I and E2 to capacitor (II) ):
  1. E1E2=9K1K2K3(K1K2K3)(K2K3 + K3K1K1+K1K2)
  2. E1E2=(K1K2K3)(K2K3 + K3K1K1+K1K2)K1K2K3
  3. E1E2=(K1K2K3)(K2K3 + K3K1K1+K1K2)9K1K2K3
  4. E1E2=K1K2K3(K1K2K3)(K2K3 + K3K1K1+K1K2)

Solution

Energy stored in a capacitor E=12CV2
E1E2=C1C2

C1=d3ε0k1A+d3ε0Ak2+d3ε0Ak3-1
=d3Aε0-11k1+1k2+1k3-1
=d3Aε0-1k1k2+k2k3+k3k1k1k2k3-1

C1=3Aε0dk1k2k3k1k2+k2k3+k3k1
C2=ε0A3k1d+ε0A3k2d+ε0A3k3d
C1C2=E1E2=9k1k2k3k1+k2+k3k1k2+k2k3+k3k1

Asked in: JEE Main 2019 (12 Apr Shift 1)

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