diff --git a/12.temporary_ins/10.electrostatics-vacuum/30.gauss-theorem-demonstration/20.overview/notion_solid_angle.jpg b/12.temporary_ins/10.electrostatics-vacuum/30.gauss-theorem-demonstration/20.overview/notion_solid_angle.jpg new file mode 100644 index 000000000..8ea7118d2 Binary files /dev/null and b/12.temporary_ins/10.electrostatics-vacuum/30.gauss-theorem-demonstration/20.overview/notion_solid_angle.jpg differ