Difficult conceptual numericals

Electrostatic Potential And Capacitance

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1
If the variation of electric potential for an electric field is given, then can we predict the electric field from the graph of Potential vs Distance? We have to keep in mind that:
"Magnitude of electric field is given by the change in the magnitude of potential per unit displacement normal to the equipotential surface at the point".
2
Any cavity in a uniform charge distribution can be considered as two solid shapes of charge density and placed simultaneously. Let's see how this assumption helps us to find potential due to charge system having cavities.
3
An electric dipole has potential energy stored in it due to the presence of external electric field. This potential energy changes as the orientation of dipole changes w.r.t. field. The work is done on the dipole to al make it at an energy is dissipated as heat while changing
5
Concept of energy stored by a capacitor:
Sometimes, the parameters like C, Q, V needed to calculate the energy (= or of a capacitor are not given directly. In this question, we calculate the charge using the area and given charge density. We have to check if the energy stored by this capacitor is sufficient to cause a spark.
6
Problems on force between plate of parallel plate capacitor:
Once we know to write the force between plates of the capacitor, we can solve any complex problem involving forces, just like we used to do it in Newtonian mechanics. This question is combination of spring force and force between parallel plate capacitors.