Question

How will the 1.energy stored and 2.the electric field inside the capacitor be affected when it is completely filled wth a di electric material of dielectric constant K.?

Answer 1

When a dielectric slab of dielectric constant K is introduced in between the plates of a charged capacitor, then :
Electric field E decreases, i.e., E = E₀/K
Energy stored in the capacitor U increases, i.e, U = 1/2 CV² = KU₀
where, E₀ and U₀ are the electric field inside the capacitor and energy stored in the capacitor respectively, when there is vacuum/ air in between the plates of the capacitor.
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