Đáp án:
\(\begin{array}{l}
a.\\
{N_2} = 18\\
b.\\
{U_2} = 55V
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
a.\\
\frac{{{U_1}}}{{{U_2}}} = \frac{{{N_1}}}{{{N_2}}}\\
\frac{{220}}{{12}} = \frac{{330}}{{{N_2}}}\\
{N_2} = 18\\
b.\\
\frac{{{U_1}}}{{{U_2}}} = \frac{{{N_1}}}{{{N_2}}}\\
\frac{3}{{{U_2}}} = \frac{{18}}{{330}}\\
{U_2} = 55V
\end{array}\)