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- PHY102 Physics II © Dr.Cem Özdoğan
- 25-7 Dielectrics and Gauss’ Law Capacitor with a Dielectric
- In Fig. 25-16a, without a dielectric. We enclose the charge q on the top plate with a Gaussian surface and then apply Gauss’ law. If E0 represents the magnitude of the field, we have
- In Fig. 25-16b, with the dielectric in place. Now the surface encloses two types of charge: It still encloses charge +q on the top plate, but it now also encloses the induced charge –q’ on the top face of the dielectric.
- The charge on the conducting plate (q) is said to be free charge because it can move if we change the electric potential of the plate;
- The induced charge (q’) on the surface of the dielectric is not free charge because it cannot move from that surface.