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    First of all how can a dielectric be 'formed'? I thought it had to be a material inserted in between the capacitor plates. If it's referring to air acting as a dielectric then can someone explain how and why this occurs please.

    Also for b) how can you find the volume of the plates when only the surface area is given?
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    (Original post by G.Y)
    First of all how can a dielectric be 'formed'? I thought it had to be a material inserted in between the capacitor plates. If it's referring to air acting as a dielectric then can someone explain how and why this occurs please.

    Also for b) how can you find the volume of the plates when only the surface area is given?
    Part a)

    Semantics.

    Dielectric material (shortened to dielectric) is the bulk material between the capacitor plates.

    A 'dielectric is formed' implies the dielectric material is polarised by an electric field developed by a difference of charge on the plates.

    The question tells us the maximum potential allowed on the plates is 100 Volts. It also tells us the maximum electric field strength before insulation breakdown occurs as 700x106 Vm-1.

    At a potential difference of 100V, the minimum distance between the plates before the field strength exceeds 700MV is

    d = \frac{100}{700\textrm{x}10^{6}} = 0.143\textrm{x}10^{-6}\textrm{m}

    Part b)

    The surface area of the plates is given as 1.6m2.

    The volume of the polarised dielectric can now be calculated using the thickness from part a).

    Finally use E_{p} = \frac{1}{2}CV^{2} and the volume of the dielctric to calculate the energy density (energy stored per m3).
 
 
 

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