Đặt điện áp u = U0cos(ωt) vào hai đầu đ...

C

- Hướng dẫn giải

\(\begin{array}{*{20}{l}}
{C = {C_1}}\\
{{U_{MB}} = \frac{{U\sqrt {{r^2} + {{\left( {{Z_L} - {Z_C}} \right)}^2}} }}{{\sqrt {{R^2} + 2rR + {r^2} + {{\left( {{Z_L} - {Z_C}} \right)}^2}} }} = \frac{U}{{\sqrt {1 + \frac{{{R^2} + 2rR}}{{{r^2} + {{\left( {{Z_L} - {Z_C}} \right)}^2}}}} }}}\\
{{U_{MB\min }} \leftrightarrow {Z_L} = {Z_C}}\\
{{U_1} = {U_{MB\min }} = \frac{U}{{\sqrt {1 + \frac{{{R^2} + 2rR}}{{{r^2}}}} }} = \frac{U}{{10}}(*)}\\
{C = {C_2} = \frac{{{C_1}}}{2} \to {Z_{C2}} = 2{Z_{C1}} = 2{Z_L}}\\
{{U_2} = {U_{C\max }} = \frac{{U\sqrt {{{\left( {R + r} \right)}^2} + Z_L^2} }}{{R + r}} = \frac{{U\sqrt {{{\left( {90 + 10} \right)}^2} + {{100}^2}} }}{{90 + 10}} = U\sqrt 2 }
\end{array}\)

Từ (*)

\(\frac{{{U_2}}}{{{U_1}}} = \frac{{U\sqrt 2 .10}}{U} = 10\sqrt 2 .\)