Variable Capacitor - Physics Demonstrations - Variable Capacitor | Physics Undergraduate Labs

Purpose

Shows that capacitance depends on conductor geometry by varying the overlap area between interleaved plates. Students observe real-time capacitance changes on a meter as the plates are rotated, reinforcing that capacitance is a geometric property ( $C = \epsilon_0 A/d$ ).

BK Precision Model 830A autoranging capacitance meter reading 154.6 pF, connected via red leads to a variable air capacitor with interleaved semicircular plates fully meshed inside a clear cylindrical enclosure

Same capacitance meter now reading 4.47 pF with variable capacitor plates rotated to minimal overlap

Figure 1: Plates fully meshed (maximum overlap): capacitance meter reads 154.6 pF.

Figure 2: Plates rotated to minimal overlap: capacitance meter reads 4.47 pF — a 97% reduction.