Tinfoil Cylinder Capacitor
Purpose
Demonstrates that increasing a conductor's surface area increases its capacitance. Charge an electroscope connected to a rolled-up tinfoil sheet, then unroll the foil and observe the electroscope deflection decrease — at constant charge, larger area means larger capacitance and lower voltage.
Figure 1:
Top: tinfoil rolled up on cylinder, electroscope needle shows large deflection. Bottom: tinfoil unrolled, electroscope deflection decreases — demonstrating increased capacitance at constant charge.