设有一长直矩形(a*2a)接地金属槽，上盖板对地绝缘ф1=10，侧壁，底ф2=0，求槽内的电位分布。用有限单元法求解。-Grounded metal tank with a long straight rectangular (a* 2a), on the cover insulation ф1 = 10, sidewalls, the bottom ф2 = 0, seeking a slot of the potential distribution. Using the finite el