Bai nay xuat hien nhiu lam roi! Goi $C_{1}=C_{2}=C$
Do hai tu noi tiep nen $C_{b}=\frac{C}{2}$
Khi K mo thi nang luong dien tu cuc dai la
$W=\frac{U_{o1}^{2}.C_{b}}{2}=\frac{U_{o1}^{2}.C}{4}$
Thoi diem dong qua cuon day co gia tri hieu dung nghia la luc $W_{tu}=W_{dien}=\frac{W}{2}$
Luc nay dong khoa K mot tu bi noi tat ma 2 tu co C bang nhau nen nang luong dien giam mot nua tuc la nang luong dien tu con lai:
$W^{'}=W_{tu}+W_{dien}^{'}=\frac{W}{2}+\frac{W}{4}=\frac{3W}{4}=\frac{U_{o2}^{2}C_{b}^{'}}{2}=\frac{U_{o2}^{2}C}{2}$
$<=>\frac{3U_{o1}^{2}C}{16}=\frac{U_{o2}^{2}C}{2}<=>U_{o2}=\frac{\sqrt{6} U_{o1}}{4}=12V$
Dap an la A