A thin copper ring of radius a is charged with q units of electricity. Calculate the electric field at a point at a distance x from the centre and on the axis of the ring. Use the result to find the electirc field due to a charged disc of surface density of charge `epsilon`.

Answer

`E=1/(4piepsi_0)*(qx)/(a^2+x^2)^(3//2);E=sigma/(2epsi_0)(1-x/(sqrt(a2=x^2)))`