Khi vat nSng di qua v i t r i can bang, chuyen dong tren cung tr6n nen hap life cua P v^ sufc cSng T tao thknh life hirdmg tam V i v^y, liic t^c dung len no khong can bkng vdri lire cang cua day Vay chon dap an D Cdu 19: Trong nguyen tuf hidro, Mn kinh Bo la ro = 5,3.10""m Ban kinh quy dao dCifng N la: D i32,5.10-"m C 21,2.10-"m B 84,8.10-"m A 47,7.10-" m Giai Ban kinh quy dao dCtog N la: r„ = n\ 16ro = 84,8.10-"m Vay chon dap an B Cdu 20: Mot chat phong xa c6 chu ky ban la 3,8 Sau thcfi gian 11,4 t h i phong xa (boat phong xa) cua liTong chat phong xa lai bSng bao nhieu phan trSm so v6i phong xa cua lirang chat phong xa ban dau? A 12,5% ' B 25% C 75% D 87,5% V i 11,4 tifdng uTng vdi chu k i T nen dc phong xa lai la: H = ^ = ^ = 12,5o/oH, Vay chon dap an A ° Cdu 21: Neu mot doan mach dien xoay chieu khong phan nhdnh, ciicfng dong dien t r i pha so vdri hieu dien the giUa hai dau doan mach, t h i doan mach gom A tu dien va bien t r d B dien tror thuan v^ cupn cam C cuon day thuan cam va tu dien vdi cam k h ^ g nho hcfn dung khang D dien t r d thuan va tu dien Neu mot doan mach dien xoay chieu khong phan nhanh, ciTong ddng dien tre pha so v6i hieu dien the giffa hai dau doan mach, t h i doan mach gom dien t r d thuan va cupn cam Vay chon dap an B 10 GiSi Chi titft