# I Cavity in a dielectric material

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1. Jun 30, 2017

Hello friends.

If i have a dieletric material ( w/ a hole) and apply an uniform eletric field on it, the eletric field in the hole will stay null ?

Peace.

2. Jun 30, 2017

### Paul Colby

No, why would one think so? The normal component of $D=\epsilon(r)E$ and the tangent component of $E$ are continuous across dielectric (actually all) material boundaries.

3. Jun 30, 2017

Not if as much $D$ flux exits as enters the volume as leaves which is actually the case. My suggestion is work a 1-D problem that's simple to solve completely. Try a 3 layer parallel plate capacitor with a void layer inside where you ignore fringing fields. Continuity of normal $D$ along with the total voltage drop yields an answer. You will find an $E\ne0$ in the air gap.