The proof plane is a conductive disk attached to an insulated handle.
It is used to sample the charge density on charged conductive surfaces.
Our proof plane consists of an ebonite rod with a brass disc having a diameter of 50mm.
Students can comprehend that how by touching the proof plane to a surface, it will acquire the same charge distribution as the surface. By measuring the charge on the proof plane, the charge density on the surface can be determined.