Đặt điện áp \(u={{U}_{0}}\cos \left( \omega t+\frac{\pi }{4} \right)\) (V)

* Hướng dẫn giải

Ta có: \(u={{U}_{0}}\cos \left( \omega t+\frac{\pi }{4} \right)\).

\(i={{I}_{0}}\sin \left( \omega t+\frac{5\pi }{12} \right)={{I}_{0}}\cos \left( \omega t+\frac{5\pi }{12}-\frac{\pi }{2} \right)={{I}_{0}}\sin \left( \omega t-\frac{\pi }{12} \right)\,\,\left( A \right)\).

\(\Rightarrow \varphi ={{\varphi }_{u}}-{{\varphi }_{i}}=\frac{\pi }{3}\Rightarrow \tan \varphi =\frac{{{Z}_{L}}}{R}=\tan \frac{\pi }{3}=\sqrt{3}\Rightarrow \frac{R}{{{Z}_{L}}}=\frac{1}{\sqrt{3}}\).