Electric field due to a line charge, surface area

[th3plan]

Homework Statement

A charge distributed uniformly over 1 face of the circular disk, find the surface charge density ?


well i know density for surface charge is S= charge/area, the area for face of 1 circular disk is what ? 2pir ?

 

[cheff3r]

area of a circle is pi*r^2
what u have is the circumference