Câu hỏi 9

P = U.I.cosφ

\(\eqalign{
& \tan \varphi = {{{Z_L} - {Z_C}} \over R} = \tan {60^0} = \sqrt 3 \Rightarrow {Z_L} - {Z_C} = \sqrt 3 R \cr
& \cos \varphi = {R \over Z} = {1 \over 2} \Rightarrow R = {1 \over 2}Z \Rightarrow Z = 100\Omega \Rightarrow I = {U \over Z} = {{120} \over {100}} = 1,2A \Rightarrow P = 120.1,2.{1 \over 2} = 72W \cr} \)