A parallel-plate capacitor contains two dielectric layers as shown: K=2 from x=0 to d and K=4 from x=d to 3d. It is connected to a battery. Which graph correctly shows electric field E versus x?
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Question

A parallel-plate capacitor contains two dielectric layers as shown: K=2 from x=0 to d and K=4 from x=d to 3d. It is connected to a battery. Which graph correctly shows electric field E versus x?

G1 Physics · Accepted Answer

The normal electric displacement D is the same through series dielectric layers, so E=D/(Kε₀). Therefore E is constant in each region and is larger for K=2 than for K=4, with a step down at x=d. This is Image 1. Correct answer: A.