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Assume there is a parallel plate capacitor connected to 5V DC source. The dielectric present in between the plates is air. Now we place a dielectric on top of plate connected to positive terminal of the DC source. (assume relative permittivity of dielectric to be 5). What will be the effect of such a configuration on the capacitance of the parallel plate? An image for the configuration is provided below:

enter image description here

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    $\begingroup$ @sammygerbil I meant dielectric is placed outside of the plates. I have provided the diagram above. $\endgroup$
    – Rupert
    Mar 14, 2017 at 11:20

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For an ideal capacitor, there is no electric field outside of the gap between them. If there is no field, there is no polarization of the medium - so "the capacitor doesn't know it's there", and there is no effect on the capacitance.

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  • $\begingroup$ what about non-ideal scenarios, where the charges are distributed over the entire surface of the plate? $\endgroup$
    – Rupert
    Mar 14, 2017 at 15:27
  • $\begingroup$ Charges will be "almost entirely" on the inside surface. The only non-ideality is that a little bit of the electric field "leaks out" of the sides of the capacitor. In principle, adding the dielectric may increase the capacitance by a tiny amount. And I do mean tiny. $\endgroup$
    – Floris
    Mar 14, 2017 at 17:09
  • $\begingroup$ See also physics.stackexchange.com/q/12309/26969 $\endgroup$
    – Floris
    Mar 14, 2017 at 17:13
  • $\begingroup$ Is there a specific reason for the charges to be concentrated on the inside of the surface? $\endgroup$
    – Rupert
    Mar 14, 2017 at 17:34
  • $\begingroup$ Of course - the opposite charges attract! $\endgroup$
    – Floris
    Mar 14, 2017 at 19:03

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