An infinite cylinder of radius a is centered on the zaxis A

An infinite cylinder of radius a is centered on the z-axis. A volume charge density rho_v = 3 rho^2 C/m^3 exists only inside the cylinder. Use Gauss\'s law to determine the field everywhere outside the cylinder rho > a

Solution

gauss law applicable only for closed surfsces

as cyllinder z axis ranging from minus infinite to infinite

it is not a closed surface hence here gauss is not applicable