Optically Worked Double Concave Glass Lens, 75mm Diameter, 300mm Focal Length Science at Home_Chemical Science Semi-stiff nylon bristle brush on

Semi-stiff nylon bristle brush on a twisted stainless steel wire handle

5 N/m spring constant

Four 153 x 76mm plates - each holding 98 iron-rod plotting compasses in a 14 x 7 matrix - assemble flat or as the faces of a cube to display 2D and 3D field-line patterns

Continuously motor-driven to supply a steady high-voltage source

Optically Worked Double Concave Glass Lens, 75mm Diameter, 300mm Focal Length Science at Home_Chemical Science Semi-stiff nylon bristle brush onLong focal double concave glass lens at 75mm diameter and 300mm focal length, the moderate curvature spreading light gently for divergence and virtual image formation work in refraction demos.