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\displaystyle U=230 V, \displaystyle P=50W, \displaystyle R=140\Omega \displaystyle Z=\sqrt{(R^2+\omega ^2 L^2)} \displaystyle \omega =314 rad/s \displaystyle (2\pi \cdot 50 = 314)

\displaystyle P=U\cdot I\cdot \cos\phi \displaystyle I=U/Z

och \displaystyle \cos\phi = R\cdot I/Z\cdot I = R/Z \Rightarrow P=U^2\cdot R/Z^2
\displaystyle 50 = 230^2\cdot 140 = (140^2+314^2L^2) \displaystyle \Rightarrow L=1,14 H \displaystyle Z=384\Omega \displaystyle I=U/Z \displaystyle I=230/384=0,60A