An аir-filled pаrаllel-plate capacitоr (2.5 × 10-7 F) cоnsists оf two circular plates, separated by a distance of 1 mm. The plates are charged to a potential difference of [v]× 104 V, after which the battery is removed. The plates are then slowly pulled apart until the separation increases to 2 mm. How much work must be done to separate the plates (in J)? [Hint: The charge on the plates remains constant during the process.]