(2)Ek=Eo-Ep Ek=Eo (x<0) E=E。- (0<x<) Ek-0 (x>a) (2) = − EEE p0k ( 0 < x < a ) Ek= E0 ( x < 0 ) Ek= 0 ( x > a ) )1( 2 2 0 2 2 0 0k a x Ex a E EE −=−= O a x Ek E0 a x Ep E0 O A ⅠⅡ Ⅲ