A parallel plate capacitor has a dielectric slab of dielectric constant K between its plates that covers 1/3…

A parallel plate capacitor has a dielectric slab of dielectric constant K between its plates that covers 1/3 of the area of its plates, as shown in the figure. The total capacitance of the capacitor is C while that of the portion with dielectric in between is C1 . When the capacitor is charged, the plate area covered by the dielectric gets charge Q1 and the rest of the area gets charge Q2 . The electric field in the dielectric is E1 and that in the other portion is E2 . Choose the correct option/options, ignoring edge effects.

  1. E1E2=1
  2. E1E2=1K
  3. Q1Q2=3K
  4. CC1=2+KK

Solution

As E=vd
E1=vd
E2=vd
(As both parts have some P.D.) upper capacitor have capacitance
C1=Kε0A/d 
Lower capacitor
C2=2ε0A/d
equivalent capacitance
C=k+2ϵ0A/d
CC1=k+2k
And E1 :E2=vd:vd=1

Asked in: JEE Advanced 2014 (Paper 1)

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