Q84 / 90 · JEE Main 2019 (09 Jan Shift 2) · Physics

A parallel plate capacitor with square plates is filled with four dielectrics of dielectric constants K1, K2, K3, K4 arranged as shown in the figure. The effective dielectric constant K will be:

Figure

  • Correct answer
    A
    K=K1K2K1+K2+K3.K4K3+K4
  • B
    K=K1+K2K3+K42K1+K2+K3+K4
  • C
    K=(K1+K4)(K2+K3) 2K1+K2+K3+K4 
  • D
    K=K1+K2(K3+K4)K1+K2+K3+K4

Solution

Figure

C1 and C2 are in series.

The equivalent capacitance of C1 and C2 is

C12=∈0A2d2K1+d2K2=∈0AdK1K2K1+K2

C3 and C4 are in series

C34=∈0A2d2K3+d2K4=∈0AdK3K4K3+K4

Ceq=C12+C34=∈0AdK1K2K1+K2+K3K4K3+K4

∴Keq=K1K2K1+K2+K3.K4K3+K4

Hence, the correct answer is option: 'A'.

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