Lag1989 task №14.16

An electron beam accelerated by a potential difference Uo = 300V, passing through an uncharged horizontal flat capacitor parallel to its plates, gives a luminous spot on a fluorescent screen located at a distance of L = 12cm from the end of the capacitor. When the capacitor is charged, the spot on the screen shifts by S = 3 cm. The length of the capacitor Lo = 6 cm. The distance between its plates is f = 1.4 cm. Find: a) the potential difference U between the plates of the capacitor; b) field strength E in the capacitor; c) volumetric energy density of the capacitor field.