Needle with plug

Combines features that significantly improve the ease of setup, the durability of the Torsion Band and the quality of results. In the newer models the spheres are tungsten rather than lead.

Allows the students observation of velocity of drop rising in an electric field, then permits calculation of the force on the charge carried by the oil drop.

Replacement torsion bands for the Gravitational Torsion Balance (AP-8215A).