Hello Tim, as one point is within the charged cylinder the field is 0. Since the flux is due to the charge enclosed by the Gaussian surface. But there is no charge inside the imaginary surface with radius ie half of the given ie 0.015 m
Okay for the second case. Let us imagine a cylinder of radius 0.06 m with some length L
So surface area of the charged cylinder covered is 2 pi (0.03) L
So the charge for this area = 2 pi (0.03) L (0.8) * 10^-6 C
Hence q /Epsilon Not is the flux coming out of our imaginary Gaussian surface.
Let E be the field (uniform) to be found out.
So be calculation the flux Integral E ds
Or E * 2 pi (0.06) L
By Gauss law , q / epsilon not = E * 2 pi (0.06) L
or E * epsilon not = [2 pi (0.03) L (0.8) * 10^-6 ] / [2 pi ( 0.06) L] = 0.4*10^-6
Required E = 0.4*10^-6 / 8.85*10^-12 = 4.52 * 10^4 V m^-1