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2. Nguoithay.vnNguoithay.vnT (*) v (**) -----> 2 = 8 ----> = 4 cm Do v = .f = 180 cm/sKhi k = 3. M l im cc tiu (bc 4)Chn p n BCu 23: Trong mt th nghim Ing, hai khe S1, S2 cch nhau mt khong a = 1,8mm. H vn quan stc qua mt knh lp, dng mt thc o cho php ta do khong vn chnh xc ti 0,01mm. Ban u,ngi ta o c 16 khong vn v c gi tr 2,4mm. Dch chuyn knh lp ra xa thm 30 cm chokhong vn rng thm th o c 12 khong vn v c gi tr 2,88mm. Tnh bc sng ca bc x.A. 0,45.m B. 0,32 .m C. 0,54 .m D. 0,432 .mGii:Ta c i1 =164,2= 0,15 (mm); i2 =1288,2= 0,24 (mm)i1 =aD; i2 =aDD )( vi D = 30 cm = 0,3m12ii=DDD =15,024,0= 1,6 ------> D = 50 cm = 0,5m-----> =Dai1=5,010.15,0.10.8,1 33 = 0,54.10-6m = 0,54.m. Chn p n CCu 24: Mt thu knh hi t mng c hai mt cu ging nhau, bn knh R, c chit sut i vi tia ln = 1,60, i vi tia tm l nt = 1,69. Ghp st vo thu knh trn l mt thu knh phn k, hai mt cuging nhau, bn knh R. Tiu im ca h thu knh ny i vi tia v tia tm trng nhau. Thu knhphn k c chit sut i vi tia (n1) v i vi tia tm (n2) lin h vi nhau biA. n2 = n1 + 0,09 B. n2 = 2n1 + 1 C. n2 = 1,5n1 D. n2 = n1 + 0,01p dng cng thc v thu knh:f1= (n-1)R2i vi TK phn k1f= (n-1)R2i vi h TK :hf1=f1+1ff1= (n -1)R2tf1= (nt -1)R2Theo bi ra fh = fht -------> (n -1)R2- (n1 1)R2= (nt -1)R2- (n2 1)R2----> n n1 = nt n2 -----> n2 n1 = nt n = 1,69 1,60 = 0,09n2 = n1 + 0,09 Chn p n ACu 25: Mt thu knh hi t c hai mt cu cng bn knh R = 10 (cm), chit sut ca thu knh i vitia tm v tia ln lt l 1,69 v 1,6. t mt mn nh M vung gc vi thu knh ti F. Bit thu knhc ra l ng trn ng knh d = 5 (cm). Khi chiu chm nh sng trng hp, song song vi trc chnhca thu knh th kt lun no sau y l ng v vt sng trn mnA. L mt vt sng trng, c rng 0,67(cm)B. L mt gii mu bin thin lin lc t n tm c rng 0.67(cm) 3. Nguoithay.vnNguoithay.vnC. Vt sng trn mn c tm mu tim, mp mu , c rng 0,76(cm)D. Vt sng trn mn c tm mu , mp mu tm, c rng 0,76(cm)Gii:Do mn t ti tiu din ca tia mu nn chm tia hi t ti tiu im F nn vt sng trn mn ctm mu , mp mu tm. Tiu c ca TK i vi tia f1= (n 1)R2-------> f =)1(2 nR= 8,33 (cm); ft =)1(2 tnR= 7,25 (cm);Gi D l ng knh ca v sng trn mndD=ttfFF=ttfff = 0,15-----> D =ttfff d = 0,75 cmChn p n DFFt