Parallel Plate Capacitors

Practice: Two circular plates of radius 2cm are brought together so their separation is 5mm. What is the capacitance of these plates?

Practice: A 3 F capacitor is given a potential difference across its plates of 10 V. What is the charge built up on its plates? If the source of the potential difference across the plates is removed, but the plates maintain their charge, what is the new potential difference across the capacitor if the distance between the plates is doubled?