de45phut
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Y BAN NHN DN QUN BNH THNHKIM TRA 1 TIT MN VT L 9 PHNG GIO DC V O TO Ngy 12 thng 3 nm 2011Thi gian 45 pht khng k thi gian giao .Cu 1: (2,5d) K tn hai b phn chnh trong mt my pht in xoay chiu. Dng in xoay chiu c to ra trong b phn no? Dng in xoay chiu c cc tc dng no ? trong tc dng no ph thuc vo chiu dng in? ti sao?Nu tn mt thit b s dng dng in xoay chiu v cho bit dng in xoay chiu c tc dng no trong thit b ny.Cu 2: (2,5d) Nu cu to ca my bin th ? My bin th hot ng da trn hin tng vt l no?Ngi ta t mt hiu in th 220V vo cun dy c qun 200 vng ca mt my bin th th u cn li c qun 1000V ngui ta c thu c mt hiu in th l U2.a) My ny l my tng th hay my gim th? Ti sao?b) Tnh hiu in th U2.Cu 3: (1,5d) Th no l hin tng khc x nh sng ?Khi tia sng tuyn t mi trng nc sang mi trng khng kh th gc khc x v gc ti nh th no ?Cu 4: (1,5d) Trong vic truyn ti in nng i xa, khi truyn ti i mt cng sut in xc nh, c th gim hao ph do ta nhit trn ng dy dn? cch lm no c hiu qu tt nht? thc hin cch lm ny nh th no?Cu5: (2d) Vt sng AB cao 2cm t vung gc trc chnh trc thu knh hi t mt on 30cm cho mt nh tht AB cao 4cm . V nh AB ca AB qua thu knh (khng cn theo ng t l ) v tm tiu c ca thu knh.