Double Concave Glass Lens, 50mm Diameter, 250mm Focal Length, 4mm Thick Physics_Electricity & Magnetism closing a circuit by inserting

closing a circuit by inserting the plug into the gap between the copper blocks

25-inch storage case

and 125mm in a plastic wallet with keepers

Sprung-tip jockey contact slides smoothly along the resistance wire of a Wheatstone bridge or potentiometer to find the null-deflection balance point during student-built bridge experiments

Extended-range rheostat at 12 ohms and 4A on a 200x44mm tube with constantan winding

Double Concave Glass Lens, 50mm Diameter, 250mm Focal Length, 4mm Thick Physics_Electricity & Magnetism closing a circuit by insertingDouble concave glass lens at 50mm diameter and 250mm focal length on a 4mm thick blank, the diverging curvature softening divergence for subtler virtual image reduction in optics work.