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Question: Answered & Verified by Expert
A parallel plate capacitor is made of two square plates of side a, separated by a distance d da. The lower triangular portion filled with a dielectric of dielectric constant K, as shown in the figure. Capacitance of this capacitor is:

PhysicsCapacitanceJEE Main
Options:
  • A Kε0a22dK+1
  • B Kε0a2dK-1lnK
  • C Kε0a2dlnK
  • D 12Kε0a2d
Solution:
1781 Upvotes Verified Answer
The correct answer is: Kε0a2dK-1lnK


Consider a small element at a distance x. It is a two capacitors in series.

dc=dc1×dc2dc1+dc2

dc=ε0.adxxtanθk+d-xtanθ1

dc=ε0K.adx-xtanθK-1+d.k

C=0aε0K.adx-xtanθK-1+d.k

=ε0k.atanθ(K-1)ln-atanθK-1 +d.kd.K

=ε0Ka2dK-1lnK

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