The electric field of a ring of charge on the axis of the ring can be found by superposing thepoint charge fields of infinitesmal charge elements. The ring field can then be used as an element to calculate the electric field of a charged disc.The electric fields in the xy plane cancel by symmetry, and the z-components from charge elements can be simply added.If the charge is characterized by an areadensity and the ring by an incremental widthdR' , then:This is a suitable element for the calculation of the electric field of a charged disc.
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Electric field in the ring is zero thats it...