diff --git a/12.temporary_ins/10.electrostatics-vacuum/30.gauss-theorem-demonstration/20.overview/solid_angle_definition.jpg b/12.temporary_ins/10.electrostatics-vacuum/30.gauss-theorem-demonstration/20.overview/solid_angle_definition.jpg
new file mode 100644
index 000000000..16c18b5ee
Binary files /dev/null and b/12.temporary_ins/10.electrostatics-vacuum/30.gauss-theorem-demonstration/20.overview/solid_angle_definition.jpg differ