Find the electric field caused by a disc of radius "a" with a uniform charge density $\;\sigma\;$ , at a point along the axis of the disc a distance x from its centre .

Question

$(a)\;\large\frac{\sigma}{2 \in_{0}}\qquad(b)\;\large\frac{\sigma}{\in_{0}}\;(1-\large\frac{1}{\sqrt{\large\frac{a^2}{x^2}+1}})\qquad(c)\;\large\frac{\sigma}{2\in_{0}}\;(1-\large\frac{1}{\sqrt{\large\frac{a^2}{x^2}+1}})\qquad(d)\;zero$