15 A parallel-plate air capacitor is to store charge of magnitude 240.0 pC on each plate when the
potential difference between the plates is 42.0 V. (a) If the area of each plate is 6.80 cm², what is
the separation between the plates? (b) If the separation between the two plates is double the value
calculated in part (a), what potential difference is required for the capacitor to store charge of
magnitude 240.0 pC on each plate?