The plates of opposite polarity are joined together after the capacitors are charged.

Question

A 3μF capacitor is charged to a potential of 300 V and a 2μF capacitor is charged to 200 V. The capacitors are connected in parallel, plates of the same polarity being connected together. the plates of opposite polarity are joined together after the capacitors are charged. What amount of charge will flow when the plates are connected, and from which capacitor does it come?

Answer 1

A quantity of electricity

flows from the first capacitor to the second.

Explanation:

Before the capacitors are connected, the charges on them are Q₁ = C₁V₁ and Q₂ = C₂V₂ . The charge remaining in the capacitors after they are connected is C₁V₁ — C₂V₂ and the capacitance is C₁ + C₂. The difference in potential between the plates of the capacitors after they are connected is V = (C₁V₂ - C₂V₂)/(C₁ + C₂). The charge remaining on the plates of the first capacitor after they were connected is

Q' = C₁V = C₁((C₁V₁ - C₂V₂)/(C₁ + C₂)).

The amount of electricity passing from the first capacitor to the second is