Cdu 27: T r o n g t h i n g h i e m giao thoa a n h sang vdfi khe l a n g (Y-ang), khoang each giffa h a i khe la m m , khoang each tii m a t p h a n g chufa hai khe den m a n quan sat la 1,2 m Chieu sang h a i khe b a n g a n h sang hon hop gom h a i a n h sang dcfn sSc c6 badfc song 500 n m va 660 n m thi thu diXac h§ v a n giao tlioa t r e n m a n B i e t v a n sang ehinh giUa (trung tarn) ufng vdri h a i bufe xa t r e n t r u n g K h o a n g each tii v a n chinh giffa den v a n gan n h a t cung mau v d i v a n c h i n h giufa l a : A 9,9 m m B 19,8 m m C 29,7 m m D 4,9 m m Giai T a c6: vdri X = 500nm t h i i , = a = 0,3mm vdri ^2 = 660nm t h i k i i i = k2i2 = - ^ = 0,396mm a k| _ i , _ 396 _ 33 k^ " i j ~ 300 " ' Gia t r i nguyen nho n h a t la k i = 33, k2 = 25 Khoang each tii v a n ehinh giffa den v a n gan n h a t cung m a u vdfi v a n ehinh giffa l a : 33.0,3 = 9,9mm Vay chqn dap an A Cdu 28: M o t lac 16 xo gom 16 xo eo eijfng 20 N / m va v i e n b i c6 kho'i lirgrng 0,2 k g dao dong dieu hoa T a i t h i d i e m t , v a n to'c va gia toe eua v i e n b i I a n li/gtt l a 20 cm/s va 23 m/s^ B i e n dao dong cua vien b i l a : A em B 16 em C 10 V3 em D V cm Giai A p dung d i n h l u a t bao toan nang iLfgrng, t a c6: i k A ^ = - k x ^ + - m v ^ =-!-kx^ +-\w' 2 2 2co' Thay cAc gia t r i co - => A = V CO — = 10(rad/s), v = 20(cm/s), a = -co^x vao bieu m thdre t r e n t a di/dc A = 4cm Vdy chgn dap an A Cdu 29: M o t l^c 16 xo treo thSng dufng K i c h t h i e h cho l^c dao dong dieu hoa theo phiTOng t h a n g dufng Chu k i va b i e n dao dong GiaiChitiStdSthiTSDH, CDM6nVatli • • 13