Question

Figure shows a sheet of aluminium foil of negligible thickness placed b/w the plates of a capacitor. How will its capacitance be affected if
1)the foil is electrically insulated?
2)the foil is connected to the upper plate with a conducting wire?

Answer 1

1) This can be taken as two capacitors in series. The plate separation is d/2 and hence Capacitance is 2C. Total Capacitance is Cs = (2C×2C)/(2C+2C) = C

Hence the Capacitance remain unaffected.

2) d becomes d/2, hence the Capacitance becomes twice the original.