Figure 10: Dialog to start an interactive drawing session. the radial variation of potential and electric field and the capacitance per unit length is given by: E r ( r ) = 91 . 024 r , φ ( r ) = 100 . 0 " 1 ln( r/ 5) # , c = 1 . 3567 Ч 10 10 . (F / m) (1) 1 . 099 To start, we will define the geometry for the numerical calculation. Run the Mesh program and choose File/Create script/Create script graphics . Fill out the dialog entries as shown in Fig. 10 . For the dimensions given, note that the solution volume covers only the first quadrant of the space. We shall apply symmetry to reduce the amount of work why calculate all four quadrants when the solution is the same in each one?
When you click OK , the program enters the drawing editor of Fig. 11 . The display includes a menu at the top, a set of useful drawing tools beneath it, the main drawing area and a status bar at the bottom. We will define the following physical regions: Region 1 : the polyethylene dielectric between the cylinders. Region 2 : the inner boundary at 100.0 V. Region 3 : the outer boundary at 0.0 V. It is important to note that as we enter regions in sequence, the present region over-writes any shared elements or nodes of previous ones. By default, the drawing editor is ready to add outline vectors for Region 1 . Click the Line tool and move the mouse cursor into the drawing area.
Note that the cursor changes to a cross and that there is an orange box showing the current coordinates. Snap mode is in effect by default, and the box moves in discrete steps to exact coordinate locations. Move the mouse cursor to the origin ( x = 0 . 0, y = 0 . 0) and then click the left mouse button to set to start point of a line vector. Then move to the end of the x axis ( x = 15 . 0, y = 0 . 0) and click the button again to set the end point. A line in the color of Region 1 appears along the bottom. 15