The capacitance between the points A and B in the following figure.

A capacitor of capacitance $$C_1=1 \mu \mathrm{F}$$ is charged using a 9 V battery. $$C_1$$ is, then removed from the battery and connected to capacitors $$C_2$$ and $$C_3$$ of $$2 \mu \mathrm{F}$$ and $$3 \mu \mathrm{F}$$, respectively as shown in the figure. Find the charge on $$C_3$$ after equilibrium has reached is

A 60 $$\mu$$F parallel plate capacitor whose plates are separated by 6 mm is charged to 250 V, and then the charging source is removed. When a slab of dielectric constant 5 and thickness 3 mm is placed between the plates, find the change in the potential difference across the capacitor.