Trong moi truong dien moi: 2 21 2 21 )( r qq k r qq kF ε ε == Trong chan khong: 2 ' 21 r qq kF = Xet ve phuong dien tac dung luc thi 1 lop dien moi co be day r tuong duong nhu 1 lop chan khong co be day ε rr = ' Khoang cach giua 2 dien tich: ε ddr +−= 1 ( ) 2 1 2 1 ' r ddr F F ε +− =⇒