The surface charge density of a thin charged disc of radius \( R \) is \( \sigma \). The value of the electric field at the centre of the disc is \( \dfrac{\sigma}{2\varepsilon_0} \). With respect to the field at the centre, the electric field along the axis at a distance \( R \) from the centre of the disc is:
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For discs, remember: centre field is maximum and decreases gradually along the axis.