Cdu 12: M o t l a n g k i n h c6 goc chiet quang A = 6° (coi la goc nho) dtfcfc dat k h o n g k h i Chieu m o t chum a n h sang t r S n g song song, hep vao m a t ben cua l a n g k i n h theo phifcng vuong goc v d i m a t p h a n g p h a n giac cua goc chiet quang, r a t gan canh cua l a n g k i n h D a t m o t m a n E sau l a n g k i n h , vuong goc v d i phucfng cua chCim t i a t